A case of bad philosophy creating a bad theology.Then the same irrationality is used to interpret Vatican Council II as a break with the dogma extra ecclesiam nulla salus and the Syllabus of Errors.He was not aware of the error in the Letter of the Holy Office to the Archbishop of Boston 1949. The Letter assumed invisible cases of the baptism of desire etc were visible. It wrongly assumed hypothetical cases were not hypothetical but objectively visible.
The good Bishop uses this reasoning. So for him Lumen Gentium 16( invincible ignorance) would refer to visible cases of persons saved without the baptism of water in the Catholic Church. For me LG 16 refers to an invisible case. So it is not relevant or an exception to Feeneyite extra ecclesiam nulla salus.
For me Vatican Council II does not contradict with the dogma extra ecclesiam nulla salus as it was known to the 16th century missionaries.
Bishop Williamson's reasoning however is the same as the liberals and the Vatican Curia.