Yeah, I see some people using "geek" and "nerd" somewhat interchangeably, but with the verb forms, "to geek" or "to geek out" being used specifically for that sort of intense, excited chatter about a fondly held and at least somewhat esoteric subject, I don't think the distinction of the terms is totally arbitrary. I'd be reasonably happy calling you a bit of a film geek, for instance, whereas I wouldn't call you a film nerd, so yeah, I think it's right to use "geek" for a focused speciality. In fact, I think when you call someone an "X geek" where X is whatever specialized hobby the person has, I think a lot of the sense of social awkwardness disappears, and the meaning tends to allude primarily to the depth of knowledge and degree of focus.

Or at least, that's what my linguistic field observations suggest. YMMV.