Yes, they are as people have said situational outfits, it also seems like the tags used for situational outfits are broken, so clothing that has nothing to do with the situation shows up. The latest ones that I have noticed are some weird outfits that are only visible in some parts of Del Sol Valley? One seems to be for celebrities while I have seen situational outfits on normal NPC's in another place in Del Sol Valley.
I have no idea why maxis are adding them, some outfits seem to make little to no sense, like the fake vampires situational outfits which spawns normal sims (not vampires) in vampire clothing during nights. Why would you ever want that?
MC Command center can remove most of them in the settings "Replace situational outfits". Since I have one save with aging turned off with 200 sims with customized outfits I find this feature/bug very frustrating.