That guys comment is very reactionary, but it isn't out of the realm of reality.
Musty looked solid in Rookie Faceoff, but clearly wasn't at all ready for the preseason this year, and was a step behind. There are a lot of core things he needs to work on, and in particular the system that Sudbury runs really reinforces those weaknesses rather than works on them, which is likely why this trade request came about. He is a good prospect, but clearly has significant work to do to play a pro game.
Gushchin on the other hand is 100% NHL ready. He was tied with Barzal for the NHL lead with 9 points in 4 preseason games this year. He should have gotten more play time last season, but now he is doing everything, fighting for the puck, finding quick breakouts, in addition to incredible skill plays.
So, could Musty still be a huge star once he gets proper coaching in a pro system, and Gushchin get overwhelmed as his body can't hold up to regular NHL time? Yeah for sure, but in the preseason, Musty was invisible at best, and Gushchin was dominant all over the ice, finishing with 5 assists in a 6-5 win against Vegas' main roster.