I can tell that the coral was recently fragged (you can see the edges on the left), and this would be the primary cause of the coral's shrunken look, but the coral is shrunken enough that the skeleton is protruding in some places and it has been that way long enough that there is brown microalgae growing on the exposed parts. This shows that the coral has been stressed for some time before you got it. Fyi, it's normal for brains to get shrunken at times. My Symphyllia and Lobophyllias both shrink up just before lights out.
Also, there is old skeleton showing on the right side of the coral, but it's difficult to tell from the photo if that is from the coral partially dying at some time or whether it just happens to be growing over where a coral used to reside. I'm going to bet the former though.
Here is a coral from the Symphyllia genus that appears to be the same species. Different color though obviously. The photo is even taken at a time when the coral is shrunken:
Here is my Symphyllia (with the tissue nicely expanded, yours should look like this once it settles in):
Here is a Lobophyllia for comparison, you can see the tissue in the middle has the same texture as the outer portion of the coral:
