Warning; this is a ramble without any real point, I just wrote it as I thought it, because it interested me.
Says whom? Prove your claim.
If he rewords his statement (as it is implied anyway) to the much more justifiable "No evidence exists for God
that I have seen", he has his own word on the matter as evidence - and at that point it isn't even an argument from authority, as he is best qualified to know what he has seen. The response would then be to either prove that he is lying (a difficult task!) or give some evidence of your own that God
does exist, and thus prove his statement irrelevant because you have given him new information.
However, the step from "There is no evidence for God that I know of" to "God is based on fantasy and speculation" is a fallacious one, because he does not necessarily posess all of the information that theists do, so he is not qualified to speak on their behalf. This is a step from his personal experience to
everyone's personal experience, which isn't really justifiable. Claims of personal experience (which many theists claim) would lead him to a deadend - he would then be reduced to arguing over the validity of the personal experience, which is unlikely to ever go anywhere. Given that we would then be matching a theists claimed personal experience with his lack of personal experience, the statement would be neither proven nor disproven. You would need objective evidence to go any further, which I suspect neither side possesses (given my stance as an agnostic atheist, you could probably have seen that one coming!).
In short; claims of personal experience (or lack thereof) can validate personal beliefs, and are often tricky to disprove. However, they are abysmal at converting/persuading others, as is hinted at by the word 'personal'.