Probably nothing, but a simple phone call could put your mind at ease. I'm not a call-the-doctor-for-everything peson myself, but when I feel that troubled inner feeling about something my boys are doing, I make sure to follow up on it.
If your mama (or dada) radar is going off, best to at least ask your pediatrician about it. Depending on how he or she wants to check it out, you can decide from there. Your ped might just want to physically examine his legs and hips (no biggie), or if there's really reason for concern order a CT or something. It'll be up to you how far you go, but at least you won't be worrying.
Oh, and either way, I'd wait a week or so and see how his crawling changes. In those early days of crawling, sometimes it takes a little time to get coordinated.
You could also try doing some baby massage, and see if that leg or hip shows any increased sensitivity to touch, massage pressure, or rotation. If so, then definitely call.