He is so confident that he might just be a troll. If he isn't he is probably the greatest example of being confidently incorrect who I've seen posted here in a while.
I really wondered that too! Not sure how anyone could actually be this obstinate in the face of overwhelming evidence to the contrary. Might very well be a troll lol
Nah. I know people like that. They just shut down and reject everything that doesn't align with their world view. No point even arguing with them at that point, just let them live in their clown world.
You can sometimes have success by asking questions and getting them to elaborate and maybe find an inconsistency or error on their own. You need to enter their reality and help them tear it down from within and be aware that they might instead just kick you out of it (so if you really want to convince someone, you'll have the most success if you can make it a pleasant experience they want to continue engaging with).
But this is a disagreement about terminology, which is purely decided by consensus or definitions, so it's less likely to have some logic that can disprove it.