Sims wear generated situational outfits during special situations. These can be festival outfits, rain outfits, celebrity outfits, fake vampire outfits etc. They are pretty much broken.
There are multiple posts on answer hq about this: https://answers.ea.com/t5/Bug-Reports/OPEN-Weird-situational-outfits-on-NPCs-Mainly-Hats-Accessoire/m-p/6904580#M66940 or https://answers.ea.com/t5/Bug-Reports/OPEN-S-NPC-Sims-wear-random-cold-hot-weather-outfits-not/td-p/6903978/page/3
If you don't mind using mods and are familiar with MC Command center you can use it to remove them. It is in the dresser module, replace situational outfits.
