Make a living means "to earn the money one needs to pay for housing, food, etc.", according to Merriam Webster´s dictionary.
The question "what you do for a living?" is a valid question, when we want or need to know how someone earns enough money to live. That´s why you recalled it.
Also, from the question one can´t infer that a question was made. It could be that the second person at hand was being sarcastic towards a statement that had been just made (that of precious hubby being a good singer)...
That is, the second person could have just said: "yeah, right!" (perhaps rolling her/his eyes) and it would work too.