No-one had the slightest reason to suspect the guy in their midst would be the next manager of Celtic. And nor did he.
He was there to watch their Champions League group match against Barcelona, and he managed to relay the story yesterday while sounding sufficiently impressed rather than gushing or corny. "I almost never take pictures but I filmed that," he said. "So many times I have looked at that film, when You'll Never Walk Alone was sung before the match. I showed my girls [he is a married dad of 14-year-old twin girls]. At that point I didn't know that this was going to happen."
By "this" he meant landing the biggest job of his life, and the accompanying hullaballoo which came with that at Parkhead yesterday. There are no half measures when a Celtic manager is presented to the media and Deila was given a thorough introduction to Scotland's journalistic mill. Celtic media, the telly and radio, the daily papers, the Sundays, the Norwegian press who'd come over to cover him; they all wanted their bit of Deila. He managed to satisfy them all with aplomb, handling an hour or so of questioning with intelligence, warmth and humour. It was good going for a man who was managing little Stromsgodset at the start of the week.
Above all he dealt with it without looking spooked or uncomfortable, even when he was paraded in front of hundreds of fans on the Parkhead steps. It was an impressive public debut. Deila sounded confident rather than arrogant, and he seemed sure of himself when he spoke at length about his determination to develop and improve players without losing sight of Celtic's fundamental need to keep winning. "I think a lot of this business is about results. We need to win games and trophies. But I have to go behind that and think 'what can I do to get the best out of the team' and really work with the culture. If we talk about developing, people say 'oh developing, we don't give a sh** if we don't win'. For me, that is what you do to win. You work with the boys and the staff and get the most from them. I'm an emotional guy. I love to win, of course.
"But the best thing I know is when you have a good performance on the pitch and you win and the atmosphere is like what is was like here for Celtic versus Barcelona. When I'm driving the car home at night, I get goosebumps when I think about it. That is football. It's fun to win, but the way to win is the most fun thing. I hope I can sit in my car driving to my apartment somewhere and feel that emotion.
"At Celtic you have to play offensive football, it is in their history. You have to develop players, like I did at Stromsgodset. When I think of Celtic I think of history, of atmosphere, of passion, of family now, of energy." Last year he was contacted about moving to Sweden to take charge of Malmo but he did not pursue the opportunity. Celtic instantly felt like a far more attractive proposition. "It is about the philosophy and the values and you feel you can be a part of it."
When Deila was a schoolboy he set his sights on life as a footballer only for his mother to encourage him to instead pursue a career in education. He became a qualified teacher, taking classes of one to 10-year-olds. When he gravitated towards playing football and then full-time football management, his mother gave him a mild telling off. "She said to me that I'd picked wrong!" he said.
Coaching, and even coach education, is the essence of what Deila enjoys about football. During his playing days he trained under-19 teams and worked for the Norwegian Football Federation in helping to develop coaches and leaders. "I love to work with people and create things with people," he said. He has been entirely comfortable working under a director of football at Stromsgodset, Jostein Flo, but remains firm in asserting himself as his own man when it comes to training, tactics and management. Had Celtic offered him the role of assistant manager - he was considered when Johan Mjallby left the club - he would have turned them down. Becoming manager was a different matter.
His appetite for football knowledge has taken him to Borussia Dortmund - their manager, Jurgen Klopp, sent a him message of congratulations and good luck yesterday - Manchester City, Liverpool, Barcelona and Rennes. Comparisons to Klopp and to Brendan Rodgers have swirled around Deila's head this week. Celtic, eager to shape the perception of their unknown new man, haven't exactly discouraged these overblown claims but Deila himself played them down. He will make his own name, he said, not place himself in the slipstream of some more famous figure. Those visits to major European clubs broadened a football intelligence which would otherwise have been limited to what he has learned from a career spent entirely in Norway. It was quietly impressive, yesterday, when he said he would not take anyone from his Stromsgodset backroom team to Celtic. He explained: "It is really important to have people who are from Scotland and from Celtic. You never know what will happen, maybe foreign people or players will come. For now, I have to get control of everything and then we will see what is best."
The Celtic chief executive, Peter Lawwell, barely left his side throughout all of this. It was an obvious ploy to shield his man from any journalistic curveballs. In truth, none were thrown. More to the point, Deila looked perfectly capable of dealing with any which might have come his way. There are no points or cups given out for how a manager handles himself in front of the media, and he wouldn't be the first to talk a good game only to crash and burn. But yesterday was still a test for Celtic's new man, and he cruised it.