To tell you the truth, I was never very happy with the way this comic is blocked. That is, I think it can confusing which side the Author is in the last couple of panels. I mean, sure, if you stop to think about it, it's evident that the Author started out on the right of the imposter, and teleported to the left side, but any comic in which the reader has to think that much about who's who and who's where should really be reworked to make it more clear. Unless, of course, the entire point of the comic is to make the reader think, which was not the case here.
That being said, the imposter has a good point. If there are multiple imposters running around, you would need definite proof that the Author is who he says he is, and being able to teleport like that is pretty good proof. Then again, looking at the later years, George is able to do a reasonable facsimile of the Author's teleport, so it might not be as foolproof as one might think.