It's hard to say from the photos whether this is an infection or not. IF it is an infection it will likely be a bit more 'cottony' (don't you love that scientific term?). Also, if it is an infection you would probably see a bunch of tissue and 'stuff' fly off it if you were to blow a bit of water at it with a turkey baster.
I have seen this type of asexual reproduction (if that's what it is in your case) many times in other corals (don't remember seeing it in Caulastrea, but it sounds like any others have). I'd keep a very close eye on it to make sure it is not an infection.