Any second-rate scholar can come up with a theory about anything...they're usually called crack-pots. This guy has in fact been labelled as one and his theory debunked.
All the greatest (in fact all professional professors of Roman history) Roman historians, even non-Christians Professor Arnoldo Momigliano(a Jew and a student of the greatest Roman historian Gaetano Desanctis) and Professor Michael Grant , were certain Jesus existed, and could prove that Jesus of Nazareth was the founder of Christianity.
-(Also many of the ancestors of Christ mentioned in Matthew 1 such as King Hezekiah have been proven to exist by undisputed scientific archaeology.)