The expression "Do you not understand?"?

This is confusing. You were right in saying no, in my opinion, but it could be mistaken either way. Saying yes could be mistaken as "Yes, I do not understand" or "Yes, I understand" and the same thing with saying no. You probably only got in trouble because he was mad, and he wanted everyone to understand but nobdy at the time actually thought it through which way to answer, if you know what I mean. I would've just agreed with what the rest of the cl had said, or just not said anything at all.