His answer is a little more profound than that .
Of course, you could say, he is teaching a lesson. However, couldn't God's prophet, let alone God Himself, teach a lesson without the insult that comes with it?
Did he
have to ask, "who is my mother?" in order to make the point? Did he
have to speak as if his mother was either equally a mother to him as the disciples, or even worse, less so?
An ordinary person we could easily excuse for such clumsiness, but someone who is God's prophet or, supposedly, God Himself?
Unless you're going to say, "he was just a man like us. Maybe he was a little bit clumsy, maybe he didn't find that important," etc, but you don't. You insist he is perfect, sinless, infallible and God.