It doesn’t look very comfortable or practical travel wear but I’ve seen less/worse in flights.
If that had been me I would have laughed, made a stupid comment like ‘well I suppose I’m just too darn hot so had better cover up’ and put on a jumper (I always have a jumper in my hand luggage as places get bloody cold).
Everyone knows that air staf Have The Power and can be very mardy, so here’s really no point in arguing with them.
Why is everything a drama with people these days? Put on a jumper - get a photo and take the piss online later.