Although the youngster was musical and had followed in his big sisters' footsteps in joining the St Roch's branch of Comhaltas Ceoltoiri Eireann that has long flown the flag for Irish music in Glasgow with such distinction, he just accepted this box that landed in his lap as his lot. He certainly wouldn't have seen it as a passport to appearances at major festivals such as Celtic Connections and HebCelt or the Scandinavian tour he has lined up next year as a result of his winning the Young Scottish Traditional Musician of the Year 2013 title.
"I think I was given an accordion and told to get on with it," he says down the line from the bus that's taking the Young Trad Tour - last year's Young Traditional Musician of the Year finalists and associates - round the Highlands and points south. "I certainly had no input into the decision. I later found out that my mother's brother had played the accordion and it might have been a family continuation thing, but it turned out to be a good choice."
With family connections around the Tyrone and Derry areas and in Donegal, Callaghan was encouraged along to St Roch's from the age of four. He started out on tin whistle and found an aptitude for music that later led him to the harp and the concertina. It was as a button accordionist that he made his contribution to the St Roch's Ceili Band, however, regularly playing for dances and parties on Fridays, Saturdays and Sundays for some 10 years.
"That was great experience and a fantastic discipline to develop," he says. "Instrumental folk music has maybe moved into a more concert-style presentation over the years but it's essentially dance music, and if you are playing for dancers you really need the necessary rhythm and the tempo. Some people get excited and speed up or they get tired and slow down, but you can't do that when the music is at the service of the people on the dance floor. It also got me used to playing in front of large numbers of people in a band, although it became a different thing when I was the focus of attention."
Despite having won a Danny at Celtic Connections with the band Feolta and recording with Glasgow rockabilly outfit The Chihuahuas the previous year, it was to try and conquer his stagefright as a soloist that made Callaghan enter the Young Traditional Musician of the Year competition in 2010.
As a harper he'd found his nervousness so crippling that he could no longer play the instrument in public.
"It's really frustrating when you love something so much but you find you don't have the bottle to carry it off," he says. "I'd actually reached the stage where I was going to chuck in music because of my nerves, so the 2010 final was make or break. I was nervous when I went on to play but I actually loved being part of that occasion. I had a ball, so much so that I couldn't wait to get out and play again. Not that winning wasn't important and I actually got some bookings on the strength of my performance."
By the time this year's competition came round, he felt prepared. He was much more comfortable speaking to the audience and his whole presentation came across as very relaxed. He still got the shock of his life when he was announced as the winner, though.
"I genuinely wasn't expecting to win and I have to say that winning has been life-changing," he says.
"My diary started filling up with gigs immediately and I was able to play at HebCelt, a festival that I would have been happy to pay to get into and just be there as one of the audience. I've been able to tick off a few ambitions, like that one and playing on the BBC Alba Hogmanay show that's coming up."
Before that he has a gig at the Scots Trad Music Awards this weekend as well as gigs with his trio and others in his role as a Trad DJ (or Trisco presenter) where he mixes and matches R&B artists including Kanye West with traditional music.
"It's just a bit of fun," he admits, "but some people have actually told me that they have taken my mix-and-match ideas into their own live sets, so if it gets traditional music to a new audience it's serving a purpose."
Paddy Callaghan appears at the Scots Trad Music Awards at Aberdeen Music Hall on Saturday