It does not matter what he believes. If he does not know that the Church is the True Church, it is he that is at fault, because he ought to know that it is. He is obliged to have found the truth of the Catholic Religion.
This individual firmly believes and practices a meaningless and false religion which will gain him nothing but eternal damnation.
This is all speculation by which to satisfy the human need for a way other than that which the
Lord has set down and reguires of each man who would be saved.
If a person's ignorance is invincible then his judgement is very different from one who was raised as a Catholic. Jesus said, "To whom much is given, much will be required." and also, The servant who knew his master's wishes will recieve more stripes than the one who didn't." The angels sang at the birth of Christ, "et pax hominis bonae voluntatis." (and peace to men of good will.) they did not sing "et pax bonae Catholicam."