I think C.A. will agree with me when I say that the influence Luffy has on most people he meets would be a result of his Haki.
Anyway, since the spoilers sometimes tend to mess up details I'm pretty certain that Mihawk is thinking that Luffy has the
potential to be the most powerful person in the sea. We already know that Luffy hasn't reached the summit yet, but the power and influence he's gained in such a short time is what caused Mihawk to recognize him as a shining star of the new age. It's similar to what he saw in Zoro when he fought him in East Blue. Luffy's willpower (or Haki) will enable him to reach the top of the world, and it's already showing with all the infamy he's gained, as well as all of the powerful friends/allies he's made. I suppose you could say that it's a fringe benefit for having inherited the "Will of D".......