A deleted folder reappeared in trash?

I'm using a M1 Mini running the latest version of Big Sur. A weird thing just happened.

I deleted two small files about 20 minutes ago and emptied Trash. I was 100% sure nothing was in Trash after that. Then, I deleted an empty folder. And when I opened Trash to empty it, there was a Garageband instrument folder that had been deleted about a month ago (I don't use GB). I checked the GB folder's "date modified" and "date added" in Trash. 3/27/2021 was the date modified and nothing was showed as the date added (only a hyphen was shown).

How is it possible that the folder deleted and emptied one month ago can reappear in Trash????? Or, did I possibly do some really really odd thing???