I think he means that the "gospels" weren't written by the Apostles to whom they're attributed. It was standard literary practice at the time to put a well-known name on a work in order to give it credibility. They are written in third person tense and none of the writers ever claimed to be one of the Apostles the stories are named after. Most of the 12 Apostles were likely uneducated and incapable of such refined writing, Jesus chose to be a rabbi, a teacher, so he was educated in that field when very young and was taught to read from the scrolls at Temple.

And it goes on from there. Out of 14 letters (books) attributed to Paul, only 7 or 8 are accepted as being written by him.