First, that pronouncement would need to have been ex cathedra and VATII contained no ex cathedra statements.
Second, the old Baltimore Catechism described three types of Baptism, only one of which was by water (the most easily recognized “outward sign” and practiced by nearly all Christian, nonCatholic sects). The other two were listed as “by fire or blood” and “by desire.” Fire or blood covers individuals who, never having been baptized by water, gave their lives for their (Christian) faith (think martyrs who haven’t finished instruction); and desire covers individuals who, through no fault of their own and while striving for goodness/holiness in their lives, were never exposed to Catholic or even Christian teaching (think remote locations, lack of education, etc.). Thus, it would follow that any entity, “church” or otherwise, that promoted adherence to natural and/or God’s law in the absence of access to knowledge of Christ and His Church, COULD be a “means of salvation.”
Um, no. Ever heard of the Ordinary Universal Magisterium? The Extraordinary Magisterium (ie. ex cathedra statements, etc) is only one way that the Church is infallible.
And no again to the BOD and BOB argument. Those have nothing to do with false religions. It is NOT the same thing as saying that a false religion is a means of salvation.