Pocket of land under sea level

A small area of land with air, grass and a flower happened to generate on the sea floor and I was able to replicate the generation by using the same seed and going to the location again.
Seed: 2019938214
Location of error: -455 46 347

If I had to guess I'd say the game is either thinking that area of terrain is above ground or attached to a dry cave entrance which where neither are occurring.