> But then I have to be their friend, and play local, or I'm rude.

I'm not saying you're wrong, far from it, but I've noticed that in Spain a lot of locals go to these language exchange events, where in other countries it's not the case. And I agree with your expectation to not need to 'pamper' the visitors.

(of course they're welcome and I've talked to some of them - though it is my impression they kept a bit distant).

Cultural clashes are hard.