The location is only relevant so far as the assumption that you're among your people is true. He's clearly not. Come on, do I really need to explain why what he was doing is idiotic and is no surprise he got smashed? You see a group of Millwall fans, you're way outnumbered, they're clearly in an awful mood, you chant "We hate Millwall" in their face. If you can't see the consequences that might arise from those actions, you're being stupid, yes. Wherever you are.
In a perfect world, he doesn't get attacked but it's not where we live in and everyone knows it, including that guy.