If a writing didn’t come directly from the hand of one of the apostles, that doesn’t mean it is a forgery. The ancient world had a different concept of forgery from what we have. What the early church did recognize, in accepting what became the canon of the New Testament, was that the writings represented the teachings of the apostles whose names are attached to them. There are early witnesses from the late 1st century and early 2nd century, that attest to some of the writings’ existence and authority. People from that time surely had some idea of where the writings came from.
I’m sure this guy knows that, and is just out to deceive the gullible.
And sell his book.