I really feel like anyone who says “it’s just snowballs” must have grown up in Arizona and only seen snowball fights on hallmark Christmas movies.
Those of us who grew up in WNY and had any practice know that a snowball can be a truly effective little icy weapon.
Either way, terrible look by the fans who did it.
Edit: and also, saying there is no rule for a penalty made me think: are you implying that if fans started throwing other objects, like cans of beer, their wives, etc that it’s just free game since there isn’t a rule in the rule book that says you can’t?