I think you would, if you want to team up with those foreign people to do things like... fighting the evil mayor or sealing the city-haunting demon, don't you think so too?
I think it's common to greet ppl, who do right now the same thing at the same place to achieve the same goal by working together, don't you agree?
Here it's even common to greet ppl e.g. in waiting room at the doctors. Or to greet ppl, working in the same company (even if there are 1000s of ppl working) just by saying "Hello" at least when passing by.
