I think the better analogy would be installing a whole new bathroom (it’s a redesign after all).
In that case the plumber could and should ask where the sink is going, even if he was only told to move the toilet.
Why? Because maybe the sewage line is over there and about to be covered over with concrete and they’ll have to tear up all of that to move it in two weeks, but the sink hadn’t arrived yet so no one told him that would move either.
The point is not that the plumber is asking his customer how he should do his job, but that he can be more valuable if told the whole scope and impact of his job.
Similarly you can’t just ask a user “how could this screen work better”, you need to watch them work so that you see that that screen isn’t even the problem - they’re clicking off of it 15 times every call - but you didn’t even know to ask about the other page.
