Well, the race happened, and it was mostly hype because Phelps wasn't actually in the water with the shark...In reality, the whole thing was SIMULATED. They apparently timed some sharks: A great white, a hammerhead, and a reef shark. Then they SIMULATED the races, with Phelps going against computer-animated sharks.
Phelps actually DID race in the ocean though, so at least there was that.
As for the results, he beat the reef shark, but he got crushed by the hammerhead, and he lost to the great white by two seconds.