These guys took over a small portion of rock. Very small, half the size of a zoa head. I’m leaning anemones but odd to see them colonize like that and be that tiny. I recall seeing them as even tinier months back as smaller yellow dots.
Those are definitely colonial hydroids. If you run a quick search of green colonial hydroids I'm sure you will return a plethora of similar results. They were a problem in my nano reef I ran years ago.
