There's obviously a certain understanding based on shared experience among the various WoW races, classes and specs, no matter what your faction. When you meet, even if you can't understand each other in chat, you might tip your hat, wave or do some other emote that signifies your recognition of a fellow traveler who is just like you were, are or will be. True, sometimes it's more of a rivalry, with the occasional threat, challenge or insult. But just as often (if not more so), there is flirting, cheers and exchanging of baby spice and hugs.
I think this is even more true for druids and particularly feral druids. My main is an Alliance bear/cat, and often when I bump into another druid while going about my business, we start dancing or roaring at each other, or some other emote/interaction occurs that doesn't normally happen with every passing stranger (if it did, we'd never get anything done, I guess). The resulting hijinks are often quite comical, but even more so if we are both in an animal form.
This seems to happen just as much when I meet Hordies as anyone else. Maybe not in a battleground (probably a good thing), but when I see another feral in passing, it seems like we become alert to each other's presence and make a quick little event out of it, then go on our way. The other races and classes are there, sure, and they certainly command my awareness and interaction as the case may be. But first and foremost, I'm checking out the other ferals. It seems there's something about ferals that makes us want to interact, be it a playful romp, chase or even the occasional threatening/rude gesture to show who's boss or who doesn't want to be messed with. It makes me wonder if this is how a dog feels in the park.