Right, he didn’t get it out of a book and he wasn’t there to hear Jesus. People told him what Jesus said. That’s tradition.
Saul (later Paul) was well aware of Jesus and His teachings from either first hand witnesses or he heard Jesus speaking to crowds but did nothing. If that's tradition then so was last nights news. He followed the party line (like Catholics do) and did not become a follower of Jesus but remained a devout Pharisee (until his conversion).