Why shouldn't he say it? It's a perfectly logical thing to say when you believe bod/bob are "heresies."
I believed the same thing when I was a Feeneyite.
Just like the Dimondites, who tap dance and declare such and such that wasn't a Dimondite has gone to Hell every time they die.
It's the logical thing to do for them.
He shouldn't say it because, having received the sacrament of extreme unction, we Catholics presume that he died as one of the faithful departed. In case you do not know what a sacrament is, "a sacrament is an outward sign instituted by Christ to give grace".
If you have faith in the power of the sacrament, then you know he died a member of the faithful departed. If you have no faith in the power of the sacrament, then continue being logical I guess.