I think it's more natural to work closely with someone of your same gender, at least when they're a stranger. I'm not blaming men (or women) for that - I'm just describing how that can lead to unintentional exclusion, which is particularly painful for students who values inclusion a lot.
Of course in the friend case I think it's more of a function of your local environment than anything else. At the same company I've experienced a large difference in the local atmosphere between the Seattle and Vancouver offices, the Vancouver office was quite a bit more welcoming and more people would randomly introduce themselves.