He's already baptized; BOD doesn't apply.
Once a baptized person reaches the age of reason, they are obligated by the graces received at baptism (i.e. supernatural faith, hope and charity) to become a catholic. He rejected (repeatedly) those graces when he joined protestantism. And he died a protestant.
You are missing the point. The argument was can a person
desire to become a Catholic and 'poof' it happens. Baptism of Desire is one example in the affirmative. Can a Protestant desire to be a Catholic and 'poof' it happens? Of course. the conversion is in the desire. If the desire is genuine, the converted Protestant will follow through with formerly becoming a Catholic via the physical sacraments. The point is, that it is possible; that genuine Catholic desire can save a soul who does not get the opportunity to follow through with partaking in the other sacraments.