I can't think of anything that would cause that to happen. Is this a regular occurrence? It's definitely POSSIBLE for NPCs go on dates, but since they have no idea how to carry them out, the date will tend to be, naturally, a bad one, since the sims involved will spend their time doing random, undirected actions and not actually driving up the date score in any way.
I have six sims total that I know of, in a neighborhood of about 250 sims.
Here are two examples:
Burglar and Mandy the Hobbyist had a bad date and both got memories of it.
Townie and Mandy the Hobbyist had a bad date and only the townie has a memory of it.
They're not actually going on the dates, though. It's not like I had a community lot loaded and these NPCs were there on dates. They just have memories of having gone on dates. There's no way they actually went on a real date, since I would have seen them do it. I hadn't even taken my playable sim anywhere after the burglary, and yet the burglar clearly went on his date after burglarizing my sim (the memory of the date comes after losing a fight to the cop).