Saying it merely to piss off the jews without believing probably is Blasphemy, but saying it unironically is a-ok, and in fact it should be acknowledged more often. Denying Christ's Kingship like the jews do *is* certainly Blasphemy.
Jesus was a Nazarene, hence “Jesus of Nazareth”. Nazareth was located north of Judea, it was a region of Galilee. Nonetheless, your main point stands, Jesus had nothing to do with talmudism…..the people who were practicing the earliest version of talmudism were the Pharisees, and Jesus rebuked them.
Christ was not a jew in the same way that a jeet isn't an American, yet we look back in time and imagine them to be the same people. https://christogenea.org/podcasts/society/exactly-why-jesus-christ-not-jew
The distinguishing feature of Judaism is not faith in God, as defined by the various Abramic religions, but jewish self-aggrandization.
Judaism is nothing but the codified narcissism of a people who believe the world ought to bow and scrape to their primitive desert tribe.
In other words, something that Christ definitely did not believe in.
Saying "Christ was a jew" is like saying "Mohammed wasn't a Muslim", because he wasn't born as one.