I'm not saying what you think I am saying. The theory that "Uber price is always independent of whether the rider has credits" is indeed falsifiable, and the experiment in the anecdote seems to do so.

The opposite claim, "that Ubers do not always charge the same rate" -- the one that logically flows from falsifying the first -- is the claim that is unfalsifiable.

Is it a valid criticism of the claim? I would generally agree with you and say not really.