Series 5 screen issue (green dots appeared)

I have noticed today that my apple watch series 5 has green discolorations in upper left corner.

I couldn’t find anyone else having similar issue.

Does anyone know why did this happen and is it because of something I did or is this faulty watch?

I don’t know for how long has this been here as I don’t usually use full color watch faces

I thoroughly inspected watch’s screen and I didn’t notice any damage to the screen from outside.

If somebody has a suggestion let me know.