The number guessing makes no sense

What number are we thinking right now?

Are you kidding?

The future Bill and Ted should not have let them even START to ask that question - they should not only have known the answer TO the question, but also that he was going to ASK not only A question, but THAT exact question.

The future Bill and Ted should have at least 'mouthed' the asking of the question while the past Ted is asking it. There's no reason to let them finish asking the question and then just answering it happily - the question itself is irrelevant, and it would've been much more impactful and convincing had they actually predicted their every line they're going to say.

Also, I think it's impossible to say the same things someone else (though technically you) had said in the past, in the same, exact way. Did they do this by happenstance, organically? It's the whole Bootstrap Paradox; you can't make alterations to the timeline, or everything will change, no matter how small the change is.

In another story, some guy that has a notebook that travels in a loop, and thus would eventually deteriorate due to its own aging, just copies the notebook at one point of the loop and lets the copy replace the original in the loop. This would never, ever work, and would destroy the timeline, no matter how meticulously he does the copy, because the copy is NOT the same, no matter how identical, and even if it was identical on atomic level (which is impossible anyway), it would still be an alteration to the loop and thus destroy it completely.

It's like if Sarah suddenly decided to NOT name her child "John", but something less generic and more interesting, it would destroy the whole timeline or reality or whatever, because the whole reason she even -has- the child is because of what 'John' did in the future.

Also, isn't this question a bit too feeble to test if someone is actually you from a different time? Shouldn't they have asked something more complicated and intimate, something no one could just easily guess?