A celebration vs a shot, idk, I'd say doing the griddy as a celebration is more over the top and taunting than a muffin of a slap shot on the EN, but both were guys putting an exclamation mark on their game ending goal. I get the feeling if Greig gently scored the EN, then did the griddy, Rielly still would have overreacted, we'll never know I guess.
You don't see guys getting speared in the NFL for spiking the ball after a touchdown or attacked in the NBA for a slam dunk on an uncontested net, those are far more comparable to a slap shot EN. I guess if the did a windmill dunk or spinorama maybe, but that would be like Greig down the Michigan (he'd have screwed it up and missed and then we'd have something completely different to talk about)
Hockey players have some pretty thin skin when it comes to stuff like that, and a scrum after a game ending play isn't that unreasonable although still dumb, but it's a false equivalency to argue every team would have done something, I'm fairly confident the vast majority of the other 31 teams if not all probably wouldn't have done something resulting in a suspension, maybe bump into him and rub him out, a little pushing and shoving perhaps at worst a roughing call or a fight.