Well, speaking honestly as a male, I'd say that he's looking for some sort of reassurance (as he's feeling lonely or just been hurt or something) or he wants something physical. Of course he may want to get back with you (and why not eh!!?), but normally a guy would say something about that when asking you out again. But I have been wrong so many times, I wouldn't listen to me!
It all comes down to what ended your relationship in the first place. But if all is forgiven, then I do think that you should call him, but make no commitments, just listen to what he has to say. This is just to see where his head is at. He could just be missing what he had. Don't give in too easily, make him work for it.
I'd say it's because he's missing you (and possibly feeling lonely) - as kozmicblue said a guy will usually want to talk about getting back together before he asking you out if that was his intention. So you really need to ask yourself does he deserve to spend time with you as a friend and also without discussing his intentions (or reasons for asking you out)? Don't read to much into it at this point, I'd probably say don't call him back and wait to see if he does call you tomorrow and what he has to say then.