I don't think it's an IQ issue in terms of him not being able to see the play at all, but it's almost like he doesn't quite recognize when he can watch and jump the play, and when he needs to get in. That's part of getting accustomed to the NHL speed, the other part is him getting used to asserting himself physically to get into better positions.
It would be too early to say if it is IQ or getting used to NHL speed, but they can play into each other. I'm in the camp that players are either smart, or they aren't. You can't really develop it. Yeah some adjustment time is needed (and we'd certainly be within that), but we're not talking massive leaps here. Smart players tend to carry that over pretty quickly. ROR on game 1 was already a smart player. Same with Kucherov, Makar, Bergeron, etc. I honestly think it is more effort than IQ here as his controller gets disconnected too often and he's not willing to battle at the level it takes currently.
On the physical side... that's just not his game. Sure he'll throw a hit occasionally, but it is more like a once every other game or every third. He's a guy that thrives when he has space to operate. He doesn't use his frame to create that space, he uses his hands, skating and reads. He's plays on the perimeter and looks for soft spots to attack. He's at his best when he's got two bangers as his sides and can filter through. If he's asked to be a dirty area guy or play a physical style (not just hits, but leaning on guys and battling), the game just isn't there. His compete and battle are just not at that level. That doesn't mean he can't be a useful or good NHL player, it just changes how he can be useful and effective.