The reason why it was the Sixth Doctor who appeared: he’s just gone through the events of the serial Timelash, in which the real Herbert George Wells (pictured) travels on the TARDIS.

And, for good measure, inside the TARDIS:

Doctor: And that’s that.

Young H. G. Wells: Was that England? It looked like England.

Doctor: Yes. We took a slight detour. That was England a few years after your time.

Wells: This is all so exciting! Time travel, I mean.

Doctor: And you’re not getting any more of it, Herbert. Our next stop is to put you back where you belong.

Wells: That’s all right, I’ve learned so much already. Do you know, I think I may write a book!