I'm not sure. I have only seen 3 of them in my life and I have 2 of them. But the other one was the same size as mine.wow! i know nothing about fire clowns, is that small for a fire clown?
Clowns and many other fish will be stunted in a smaller tank just like goldfish.
Goldfish can get to a foot or more in a lake but in a small bowl don't grow much. Clownfish have similar growth habits.
In the sea they get rather large.