Nope, its not unbelievable that he didnt get bittten. Its dramatic footage, and yes surfers do get bitten, but its extremely rare for a shark bite to occur.
I like what Cape Cod is doing. Tagging Great whites and tracking they location. Shark attacks are rare. But their increasing and risk are rising. Australia has and is know for shark attacks against surfers.
I believe the surfer later said he believes the shark actually got caught in the leash attached to his ankle from the surfboard rather than trying to attack. In the video you can see the board get pulled under from the back.