I heard a sound, turned around, and looked up down

There were seeds floating in the water. I HADN'T PLACED/BROKEN A SINGLE BLOCK since generating the world for the first time.

I also heard some vine sounds and saw random vine breaking particles.

My guess is that a change in the world generation algorithm caused blocks to be mismatched with the terrain (seeds, farmland; vines, trees).

sorry for the Revenge reference