Lots of GT kids cross groups and have situational friendships: a chess friend, a friend at lunch, a friend to play outside with, etc.
That makes lots of sense to me. That is completely how my DS4 is. He loves people, all different ages. It seems when we go on playdates the other children are a little more excited about him that he is about them. He is a very likeable kid...but has certain friends he acts certain ways with. Some he just runs around with and acts goofy, some he plays board games with, some he builds things with, etc. He is pretty open to new people and new things...but he doesn't get attached. he would never say to me "when is so and so going to come over again" He doesn't miss people and doesn't talk about them much when they aren't around. Although he always knows the names of everyone and little details or facts/stereotypes about them...like "Lily likes princesses, that is all she ever wants to play with or talk about" or things like that. He doesn't seem interested in the whole "best friend" thing.
Although not like him...I too am a very social introvert, and DH is my true best friend. I have some close friends, and friends that I considered "best friends" growing up...but don't really need to be around them much to survive, LOL. And I get along with pretty much everyone and mingle among all different groups. I have always been like that. And I don't think it's a bad thing at all. I don't feel that I missed out.