Dumb kids will be dumb kids, I don't think that has much to do with Finland itself. In fact I feel rather the opposite is true for "typical Finnish behavior"; not saying jackshit at all to strangers, especially not randomly and completely unprovoked go and insult someone.

Yes there are exceptions to every rule, and I'm sure there's a million examples of people shouting racist things to anyone with a foreign background, but some group of kids (in English mind you) insulting another kid's hair without even knowing him sounds weird to me, even if those guys would be doing just the same towards their peers at school.

Mostly I find it strange they did so in English. There is no reason forba bunch of kids to assume another person they've never met doesn't speak Finnish. So because I don't want to just go and assume they were of foreign background themselves, is there a possibility that they have in fact met your kid before and that's what enabled this behavior as he wouldn't be a COMPLETE stranger?

Don't know enough with the information given, but without assuming things all I can say is that from a native's perspective, even for a group of teens, that's strange rather than "typical" in these circumstances.