Benchley only exaggerated what happened in New Jersey in 1916. A White Shark started munching on swimmers along the shore and eventually ended up in Matawan creek where it took an 11 year old boy and killed an adult. It also injured another man before two men fishing killed it.
I don't think the 1916 shark turned around and went after one of the men who fed it a ham from a dock, which I suspect was one of the more incredible scenes that Benchley was referring to.