I caved and looked it up. Apparently some Swedish people in 2012/2013 started a FB group denying the existence of horses and saying they were a non-existent fruit. There was at one point a store selling Horses Don't Exist merch as well.

https://www.horsenation.com/2013/02/01/235000-swedes-cant-be-wrong-horses-do-not-exist/