Joseph was originally supposed to be Magneto without his memories after fatal attractions, a Magneto who ressembled his AOA version, then he was retconned into being his clone because of the lack of acceptance in the fandom and his origin was that he was made to kill off Magneto, so I could see Sinister giving life to him as a way to fight off Magneto but I donīt believe the X-men or Magneto would blame him for the EMP it didnīt happen in comics canon and I donīt believe it will happen in the series, thereīs a big possibility he wonīt even appear given the circunstances that gave origin to him are not there given Magneto keep his memories and his time being comatose was very short.