I'm not surprised that was kept as a penalty. I've seen that before, and the debate ends up being that the shot was already taken, so how was there an impediment, but just because the shot was taken doesn't give you license to barrel into an attacking player. The question to ask is "is that called a foul" otherwise outside the penalty box, and I'm pretty sure that would be a foul, so just because it's in the box doesn't mean it's not a foul here.
I'd hate to see it given against us because I hate any penalty given against us, but I don't think it would be unjust.