Chickens Spawned on Farm

Hi 👋 Ive never posted here before but I had the strangest thing happen.

Im in a vanilla, single player game and 2 chick's and 1 duckling randomly spawned on my farm. Ive had a STAGE ONE coop that was fenced in so I could buy some. But I walked over and there's animals there! You can't even buy ducks until your coop is upgraded so thats even weirder. Has this happened to anyone else?