Way too early to label him a fourth line player. He's 22 and has 60 total NHL games. He's not obviously defined as a guy with any specific role yet imo.
And the talk about his ice time being the main reason he's been scoring kind of rests on the idea that anyone can score with enough ice time. Obviously that's not the case.
Absolute best case scenario, he becomes a Wilson type who can roll with top 6 lines, be a distraction and mismatch for the other team and not hold back more skilled players from doing their thing. That's not the most likely outcome, but that's still a possible ceiling.
Most likely, third liner 15-15 or 20-20 type who provides energy and is a horrible pain to play against.
Him being a career fourth liner wouldn't be totally shocking or a waste to me, but it's way, way too early to say that's where he'll top out with any level of certainty.