Jesus did not follow a religion, he was the religion
The Hebrew scriptures were not the "only scripture he knew"
He was the word made flesh, bringing a new testament because the old was no longer sufficient
He was famously challenged by Jewish authorities for not keeping the Sabbath, to which he replied that the Sabbath was made for man, not man for the Sabbath
Christ rejected the pedantic observation of law as a true path to God, which is what Judaism had become
Paul told us that there was no longer Jew nor Greek, only the Christian church
Judaism is no longer a legitimate religion, it is no longer a path to the one true God, saying that Christ was a Jew (as opposed to a Christian) is to reject the gospel, it is simply false doctrine