I think you should be cautious of just how much faith you’re putting into this person.
They said they’d agree
They didn’t. They only gave reasons to not agree. They implied that they would agree if that condition was met, but that’s not what they said.
they accepted that the person who owns the car is a Nazi
Again, they didn’t. They said, “I missed that,.my bad.” They didn’t change anything about their argument from this information (that was always available to them), just acknowledged that they didn’t use it.
Maybe I should’ve called their argument a strawman argument instead, but the discrepancy between what they say OP can call a Nazi and what they can call a Nazi feels wide enough to change the rules of the debate for each side.