Yep he's a clone:
In the meantime, Joseph investigated his past when he sought out the Acolytes, and actually assumed the role of Magneto to protect them from Humanity's Last Stand. However, he denied them when he discovered that they were planning on attacking humans again. However, when Magneto resurfaced as an independent entity, Joseph's entire identity was called into question, and he joined Sabra on a quest for answers. While in Israel, he was approached by Astra II, a villainess who revealed that she had created "Joseph" from Magneto's cells. She had hoped to use him to destroy and replace Magneto, but although Joseph was more powerful, he had failed to kill Magneto once Astra left him on his own. During that battle, Magneto hit his clone in the head with a rock, leading to his amnesia
Here's the site: http://24.191.192.76:8000/joseph.html