Well, many corals are usually called many things that they really aren't =P...it's just that the species are related so they just dub them as so-and-so. And many people nickname corals differently so it really depends...
Check out this link:
http://www.frags.org/memberfragdetails.php?fid=1635
That's a favia, but the common names listed are: Moon Coral, Pineapple Coral, Brain Coral, Closed Brain Coral, Star Coral, Golfball Coral
So yes, it is a moon coral but it's specifically another species...moon coral is just a nickname which could apply to a couple different species.
I'm almost positive it's not an acan...but I'm no expert on it. I'm pretty sure it's a favia.