Answering a question with a question

[advoca]

There is nothing wrong with answering a question with a question.

For example:
"Do you love me?"
"Ah, what is love?"

"How can I learn English?"
"Do you mean spoken English or Written English?

[zubair]

Is the below question and answer incorrect because a question has been answered with a question - if not then how else is it incorrect?
“Is John ill? He’s lost a lot of weight.”
“Yes, he is rather slender these days, isn’t he?”

yes he is he need to jog a lot