Ignoratio elenchi plus a curious pattern of argument :
Because the majority of students understood the question in a certain way, and this is the way I intended, therefore the question is not inherently flawed.
This plainly overlooks the possibility that neither the teacher nor the majority of students failed to recognise an inherent flaw.
Imagine this scenario. I ask a group of people, 'How long did it take the train to arrive ?' Most of the group reply, 'Five minutes', and I agree with them. You then claim that my question was inherently flawed. 'It can't be,' I reply, 'most of the group got the right answer.' Here my response and the majority view miss the logical truth that it cannot take any time to arrive. The journey may have taken five minutes but the arrival was instantaneous, durationless.
The same would have applied if I had asked how deep was the surface of water in a bowl. The majority of the group might have offered a micro-measurement which was just what I wanted. The question is inherently flawed even if I dismiss your objection in the same way. A surface has no depth; it isn't logically the kind of thing that can have depth.
Not only am I guilty of ignoratio elenchi in replying as I did in both cases, since I did not answer your question with a logically relevant reply (instead 'proved the wrong point'), but I and the majority of the group did not recognise logical errors when they were inherent in the questions - and blatant.