I wouldn't pretend to know Kaz and his true intentions because I obviously do not know the man, so I can only judge based on his previous actions and public statements.
The only statement he's ever made that could even possibly be described as anything close to anti-MT is when he said GT Sport wouldn't contain any. However, he didn't elaborate in the same way some other anti-MT devs have. He didn't say he was staunchly against them or anything of the sort, and we all know the u-turn that came when GTS did add them.
I also like to go back to GT HD because the business was very different back in 2004. DLC as a concept existed as far back as the Dreamcast but it was not prevalent. PC games had updates that were in the form of completely new discs you bought in the shops. Most games were not even online at all, and if they were, the concept of MTs or anything similar was not prevalent at all. I'm sure they did exist in some form in PC games but it wasn't something that publishers industry wide were pushing.
So when Kaz got up on stage and told the world that GT HD would feature an iTunes-like service where pretty much all cars and tracks, as well as features like damage, would be sold separately at a huge cost I cannot believe that was anything to do with Sony. Sony didn't even have their own digital music store back then, they were busy sticking rootkits on CDs, so I really can't believe the idea was foisted upon him. He saw the new shiny iTunes service, and liked the idea to sell digital cars.
He just strikes me as someone who sees something he really likes and gets an impulse to add it to GT. Remember GT6, with the three stars system?
We got that because Kaz in development had got obsessed with the mobile game Bad Piggies. Guess what system it had?
Also worth noting there in that interview he says he loved his iPad and iPad games in general. Guess what iPad games are full of? MTs, FOMO and random rewards/loot boxes....
Again, there is also the lack of evidence of Sony generally pushing their studios to include systems like this. Horizon Forbidden West launched at essentially the exact same time as GT7, and it doesn't have any shady practices like GT7. Sure, it's not a live service title nor does it have multiplayer, but there are still plenty of ways Sony could've forced monetisation into it. Just ask EA. But they didn't, nor have they in any other first party Sony titles. MLB The Show remains the only other current game with MTs.
In short, until I see any clear evidence of Kaz stating his personal dislike for MTs, FOMO or random roulettes I'll have no choice but to believe they were all his decision, or at the very least, he happily signed off on the ideas from his dev team and wasn't forced by Sony.