I get the feeling that you misunderstood what they were trying to communicate and prioritized literal word usage over context. They should not have said "quite authoritatively". Using "quite correctly" would have been better. "Authoritatively" was a sloppy substitute for emphatic correctness.
I acknowledged upfront that the tourist could well be correct. That addresses the possibility that it was merely sloppy wording with that intended meaning.
Looking again at what you'd put earlier, your acknowledgement very much seems to have the not-total-impossibility of them being correct as a throwaway caveat, not as a real consideration of the situation in any sense. I suspect that it being used now to address that they were using sloppy wording is a retroactive understanding after I pointed it out, and by luck is a plausible explanation.
