As one who grew up there in the period depicted, I can assure you that Van Morrison was no one's 'soundtrack' growing up in 1969.
His only album that had been released in the UK at the time was 'Astral Weeks' in 1968, which became something of a fringe/cult item in the USA, but went virtually unnoticed in the UK, having been thoroughly dismissed by UK music critics at the time, with, in fact, some thoroughly scathing reviews. Even when interest in him began to peak in the mid-'70s, the albums that everyone was playing were 'Moondance', 'His Band and Street Choir' and 'Tupelo Honey' with 'Astral Weeks' still being considered a "difficult", rarely mentioned album (although with maturity it became and remains my favourite).
That's not just narrow personal experience, as I had a Saturday/school holiday job -that eventually became full time- in one of the town's main record shops before and when the interest in Morrison began to creep on and the first album of his I recall selling insignificant quantities was his live album 'It's Too Late To Stop Now' in 1974, which garnered interest following his return to the UK and Dublin stages the previous year, with a series of rave reviewed concerts. And even then, when I say "significant quantities" I mean maybe a dozen or so a week, which made it a huge seller in comparison to his previous releases. Indeed the aforementioned albums only began to shift in any noticeable quantities, following the success of 'It's Too Late To Stop Now'
Even then those listeners were "hip" music/album buyers, as Morrison was virtually never played on the radio at the time. Indeed when I began to get into his music, most of my friends' reactions were "Van who?".
His best known solo recording, 'Brown Eyed Girl' in 1967, went totally unnoticed outside the USA and never even hit the local Northern Ireland chart, let alone the UK chart at the time and only scraped a lowly Number 60 when it was reissued in 1973 following the success of his UK and Dublin concerts, where it began its new lease of life as a 'Golden Oldie'.
My paternal grandparents knew his family and the only thing I knew about him around 1969 was the recollection of a few of mentions by my grandparents about how Margaret's grandson Ivan was making records in America now. I was aware of course of 'Here Comes the Night' by Them which was a big UK hit in 1965, but wasn't even aware that was Morrison until much later when I became aware of who he actually was.
So yes, an unusual choice for a soundtrack to 1969 Belfast.
At least we can be thankful for small mercies I suppose, that his current loony anti-vax rants won't be on the soundtrack.