You should generally but not always read any statement by Socrates in a Plato dialogue as a statement that Plato is putting into the mouth of Socrates, not something Socrates himself said. There is a gradation, though. The Apology was probably very close to what socrates actually said, and some of the later dialogues (The Republic, for example) probably bear little relationship to anything Socrates said.

But, and this is important, Plato almost certainly did not agree with everything he had Socrates say in every dialogue. Sometimes he is just playing with ideas. Personally, I think Plato is just being provocative about books in this dialogue to push an idea as far as he can.