Thats a fallacy. Protestantism is denial of Catholic dogma (articles of Faith). The SSPX haven't denied any articles of Faith. Therefore, they cannot be Protestants. At least you haven't gone to the point bornacatholic did i.e.; making up words and being silly.
Well, by that definition, Eastern Orthodoxy would be a form of Protestantism. I think it'd be best to confine the use of that term to those bodies without valid orders and sacraments.