So you don't think they recognize others of the same breed?
No, I think they recognize the scents of other dogs and people they've met before.
I think if they don't play the same with dog A versus dog B, they are picking up on the tenseness/nerves/whatever from their owner.
Great example, my little dog is almost blind. He can't see anything at night without the lights on. A lot of times at night/dusk I wave at my neighbors and keep on going and he doesn't notice a thing. So if you were to come by walking your dog, he wouldn't see you or your dog, and would keep on walking beside me.
If I were to tense up and think to myself "oh no who is this with their strange dog - is that dog leashed?" etc. he'll begin acting the bad ass and start barking.
Also on the other end of the spectrum, he still doesn't see you and your dog, but I recognize you and call out "hey Cowgirl and Cowgirl doggie" he picks up on my enthusiasm for seeing you and your dog, wags his tail, barks a little in excitement and waits for someone to sniff his butt so he can "play" with them.
It's not that a dog "knows his kind", but he knows his/her owner and their emotional cues.