The kid's explanation is suspect, at best. There's no signed contract. And there's apparently no other proof of this supposed offer from the assistant coach - only the kid's word (and the word of his representative).
On top of that, he went on to play 3 games for them before deciding to walk away. And not just any 3 games -- 3 games in which he and the team were incredibly successful.
It's more likely to me that he played the 3 games (the maximum he could play before giving up the chance to redshirt) and turned some heads - and then got thinking that either UNLV should pay up or that he'd find more money elsewhere.
If you don't have a signed agreement, then you don't have a guaranteed NIL package. And if there wasn't a signed agreement, you'd think he'd at least have e-mails or texts that indicated such a promise was being made. There doesn't appear to be any of that.
I'm not buying it.