When John asked him about having a girlfriend, Sherlock could’ve said ‘no’ and that would’ve been it, but he CHOSE TO SAY ‘NOT REALLY MY AREA’
A team of professional actors, writers and directors all agreed that yes, this needs to be answered in just that way.
AND THEN he said “no” to John’s question about whether he had a boyfriend. He could have said “not my area” to that too, but HE DIDNT.