That’s not really true (neither is the original generalization). Hockey players would have no reason to focus on getting jacked or having a bodybuilder physique because a barrel chest, massive triceps and huge shoulders isn’t going to make them any faster or really effective (it’s really a purely aesthetic pursuit), but building bigger, stronger quads and core will directly relate to speed and torque. Of course, the training has to be sport specific as well. Doing hundreds of sets of leg extensions will blow your quads up and give you the size, muscle separation, etc. that a bodybuilder is after in their quads, but it won’t really make you faster. Doing things like explosive squats, pistol squats, power cleans will also make you bigger but have a more direct correlation to making you faster and more explosive.
It should go without saying that this is combined with explosive skating drills and lateral movement drills to ensure that muscle gains and conditioning are kept abreast of one another and the muscle is being utilized as intended, while the essential movements (stop, start, skating stride, edge work, crossovers blah blah) are constantly being reenforced. It’s all kind of useless if you become more efficient as doing power cleans than skating.
So, yes, assuming he’s training under some sort of guidance (which we assume is professional and intelligent) than we can assume any added muscle will be to muscle groups that would positively effect his performance, made through athletic movements that lend themselves to better results. I doubt he’s not doing sport specific training to optimize performance, so whatever muscle he gains should not be detrimental and should only make him faster and stronger. On the side, it probably won’t make him as aesthetically “jacked” and proportionate as if he focused on bodybuilding, but combined with good nutrition will still result in a better physique anyways.
But in the generalized sense, training unsupervised and without a sport specific approach just to “get bigger” could have, probably not a noticeable negative effect on performance, but a negligible one. Just going to the gym and doing a bro split so he could have some boulder shoulders and get a sick arm pump probably wouldn’t slow him down or hurt his performance, but it wouldn’t really enhance it either.