I noticed that too, but I have to file it away under ‘writers being clever.’ John doesn’t know it’s Sherlock, so he can’t be quoting that line back to him deliberately. And wine and asking someone about their relationship status aren’t really comparable.
I suppose you cold claim that it’s being used as a calll-back to the last time John made a serious relationship commitment. But if so, considering that no one but the writers and viewers are privy to that parallel, then it’s being used in a sort of vague symbolic metatextual way, kind of like “Oh, anytime you see the character wearing green socks you know someone on the show is about to die.”
On the other hand, it may be an example of how in-jokes and phrases between close friends can make a permanent home in your vocabulary. So you could, if you wished, entertain the headcanon that they have a history of throwing that line at each other whenever asked to do something they don’t understand or don’t want to do.
“Sherlock, do the dishes before the mould colonies form feudal societies.”
“Dishes? Not really my area…”
“Damn, I need to take this phone call. John, I need you to hold this pipette very, very steady and drop precisely 1 cc of necrotizing venom on this skin sample precisely every five seconds.”
“NECROTIZING VENOM IS NOT MY AREA.”