You are why reddit sucks lol, you've got 25 words in a still image and absolutely zero context but of course that's enough for you to form an opinion and argue it's correct. Even labeling the OP a total piece of shit.

YOU DO NOT KNOW THEIR RELATIONSHIP, this could have been a perfectly acceptable, even expected response formed through years of friendship. A traditional response of sorts, like banter, etc but that thought isn't even a possability because you have the capability of feeling superior to someone by ignoring all reasonable scenarios and instead making wild assumptions and applying your own humour / friendships to form a conclusion from nothing.

This shit happened in my friends group a TON in 2012, peak "your mum" jokes in our group and unfortunately a mate lost their mum. We had like 2-3 months of "OH SHIT SORRY" moments, almost everyone had 1, some people had 2. Shit happens, we're all still best mates but i could screencap any one of those and you'd sit there and argue we are all total cunts.