Whats the system Specs/PSU?
What Driver version?
Does he have the Cap Profiles?
Did he have another video card other then the 7750/70's in the system?
Due to the lack of info, I can't provide an answer for ya, We will need to know all of the above to answer your question. Some games don't like crossfire, some do, Sometimes a driver setting in CCC could effect the FPS a lot, Or it could be a Power supply thats not able to provide enough power, could also be the CPU bottle necking the cards (Old timer CPU, People forget that too old of a CPU can seriously effect Video card performance, Crossfire will put more load on the CPU then what a single card does).