“The Catholic belief is that all salvation comes through the Catholic church. “
No; the Catholic belief has always been more specific, i.e., “there is no salvation outside the Catholic Church”.
Actually, the saying you are quoting is “Extra Ecclesium Nulla Salus.” There’s no mention of the word, “Catholic.” Even at the time the Council of Trent wrote that, there were churches other than Catholic which were not anathematized. Orthodox, Coptic, Nestorian and other Oriental churches were recognized to have effective sacraments, and, although in schism, are part of the same Body of Christ.
Unlike these churches, the Protestant churches of “substantially defective,” meaning they are cut off (”defaced”) from the “substance” of the Church; they lack proper sacraments. Therefore no Protestant may be assured of his salvation, regardless of whether he has sincerely participated in his church’s worship. However, a succession of popes has reiterated that as distorted as their view of Christ may be, because Protestants in fact worship Christ, they potentially may be saved through extra-ordinary (as in, “beyond the normal”) means.