Assuming somebody is wrong because they can't or don't answer your argument is the 'argument from silence'. Assuming that something is wrong because you can't understand may be a form of the 'argument from ignorance', although Phage did offer the choices of "cognitive dissonance" and simple outright "denial" too.
Just because you can't answer doesn't mean they're right. For example, a creationist might argue about geology from before The Fludde, when you're a marine biologist debating him on evolution in cetacea. Completely offtopic and something you have no idea about, and in any case it's a rabbit hole. So you would reasonably enough just ignore it, and attempt to continue a discussion about evolution in cetacea.
The creo would of course take that to mean you acknowledge The Fludde happened and that therefore the Bible is right and that therefore evolution isn't true, but hey, that's another story.
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