The Scotland under-21 striker joined Standard Liege this week, with Deila saying Watt had not shown enough of an improvement in his application during training since he took over at the club in June.
However, Watt was surprised by those comments and maintained it was his own choice to return to Belgium, where he spent the last campaign on loan with Lierse.
Watt said: "I read what the Celtic manager said and I do not understand it. He assured me he was very happy with my training and work, but I just wasn't in his plans because he was looking for a new striker.
"I did everything I could to convince him of my ability. I knew Standard were interested for months and it's a great opportunity for me.
"I had to get out of Scotland to aid my development. If you have any glitches in your career, they call you a bad boy who creates problems."
Deila's attempts to offload another Celtic striker, Amido Balde, have hit a snag after Standard Liege's rivals Lokeren, who are interested in signing the Guinea-Bissau international, said the Parkhead club are looking for too much money.
The 23-year-old has been a huge disappointment since his £1.8 million move from Portuguese side Vitoria Guimaraes last season.
And although the Belgian top-flight club want to take him off Celtic's hands, they are not prepared to pay the £1.5 million asking price.
Lokeren sporting director Willy Reynders said: "I know Balde well from his time at Cercle Brugge and Vitoria Guimaraes.
"He fits the profile we are looking for. But to me he seems to be on the expensive side.
"I don't know whether it is possible to do a loan deal with Celtic either.
"But we're not going to rush into things - we will weigh up all the options."
Balde managed just three goals last season in 20 league appearances, although 17 of them were from the bench.