I'd almost certainly ask my son that. Seems like a good way to get them talking about the issue, and hear any mitigating factors they might consider. A teacher who took that as a me questioning their authority ... grow up and deal with it.
Bottom line: not only is it a good way to engage with the child, sometimes the teacher really is making false accusations.
The reason that the teacher sees that repeatedly is that its an effective technique. It establishes a level of trust between the child and parent--the parent is willing to hear out the kid. And it immediately puts the kid in a tough position unless s/he fesses up to the misdeed. Getting buy-in from the child about the legitimacy of what's happening is very useful when trying to figure out how to deal with it.
Of course, implicitly by asking for the kid's word that this happened the parent is opening up the possibility that the teacher is lying. But it's necessary, and even if the kid rejected it I'm sure most parents would almost certainly still believe the teacher's narrative. It's just a pro-forma verbal tactic to get appropriate buy-in from the child. I'm not surprised that a teacher would superficially feel a bit miffed by that, but they should understand and (however grudgingly) accept the reasons its helpful.
> Well, of course it's true. I just told you.
Teacher, to parent: "(You need to listen to me.) Who do you think knows your child better? Me, or you!?"
Asking the child if what the teacher said is true is seen as an affront on the author's character as a person, not as a teacher, so it's reasonable for them to take offense at the accusation.
It's entirely reasonable not to trust the teacher's authority by default--I'm not challenging that. I'm only defending the author's position on taking offense to being challenged on something that was just said.
The very act of doing this seems to irritate the author - which I find very disturbing. Trust, but verify, is the principle here.
Hearing the student's opinion is valuable on its own, and parents don't ask to test the integrity of the teacher.
Also, it has some value by making the student admit his actions.