IMO that challenge was a 50/50 decision but I would've challenged it as well probably. In a game where the stakes were higher, maybe not. Also I wasn't there - if it looked very clearly offside watching it by the rinkside and then the overhead view sort of half-confirmed that, that would affect the decision because in that case it would seem very likely the linecam they use for the reviews confirms it 100%
I have to say I don't like the challenge rule AT ALL. If a play is worthy to be challenged (like that one clearly was), a penalty for failing challenge is really harsh. Also I don't think reviewing offsides belongs in hockey. It's very very rare you see a blatant offside not being called, all of these challenges seem to be about half inches. Yeah, maybe sometimes it WAS an offside, but **** happens and play goes on. It very rarely makes a significant difference on a play if it was offside by half an inch. I don't think the offside rule was created for nitpicking about .5 inches nor needs that kind of accuracy to do it's job.