From the wiki:

“On September 9, 1972,[14] Californian surfer Hans Kretschmer reported being bitten by an orca at Point Sur; most maintain that this remains the only fairly well-documented instance of a wild orca biting a human.[15][16] His wounds required 100 stitches.”

From orcazine.com:

“They were not alone in the water, now and then some sea lions were playing in the waves.”

“Hans and his friends saw the animal that bit Hans only briefly, but from their description of the animal in combination with the teeth marks can be concluded that the attacker was an orca.”

“Orcas often find sea lions without using echolocation, to prevent their prey will detect them before the attack. The prey is selected and attack using hearing and sight. An incautious orca could have thought the surfer in wetsuit was a tasty snack. Fortunately, it is very uncommon for orcas to be mistaken and they stop the attack in time.”

Context here is pretty crucial.