“the multiverse is a natural consequence of such eminently falsifiable theories as quantum theory and general relativity. As such, the multiverse theory stands or fails according to how well these other theories stand up to observational tests.”
That seems to me to be the fallacy (denying the antecedent). Not that it matters much to his overall message.
I agree with your point about cognitive biases and psychology. With straight up yes/no true/false questions using the hypothetico-deductive method, these things are less important, I think—but when you switch to degrees of belief and plausibility, you really must have a good meta-understanding of your own reasoning.
I think you muddle through some things in point (3). You already know the questions you would ask, because you already know the answer which was reached.