She did not explain what she saw as problematic. Maybe that a couple in a relationship situation was shown or that an attractive woman was in the foreground, or that the man openly expressed his attraction towards the other woman. I apologized profusley and tried to explain that I'm not an insensitive or sexist person, which she seemed to imply with her remark though.
I have been thinking about this incident for several days now, as I really can't make up my mind if I did something wrong or not by including the meme. If anyone want to add his/her opinion I'd be grateful therefore. The lecture was directed at B.Sc. students at a university in Europe BTW.
Personally I can say it feels quite bad being called out like that, especially as someone who has never (consciously) done anything discriminatory against women or minorities. And as someone who's quite sensitive I can say that it definitely has a chilling effect on me.
[1] https://twitter.com/annaegalite/status/1166446645204213760