What if he hit him with it? I don't see how you could NOT charge him with assault then. It seems somewhat reasonable that throwing at, but missing, could be considered attempted assault. There'd be no other target or reason for him to throw the can, really.
Anyhow, I'm fine with him being made an example of, even if the punishment seems a bit harsh. That kind of nonsense should never happen, period. It's dangerous. The lifetime ban is definitely warranted imo. The only argument should be the necessity of an attempted assault charge.