The conversation was always 100% focused on what I could prove in the moment. The general form of his argument was a radical skepticism. If you question the vast majority of people enough you will be able to find a place where they are not solid on the science. He would expertly find and exploit these areas. He was also very conspiratorial, specifically believing that NASA was a government plot to hide government spending that was going towards a corrupt elite.
He was also amazing at not understanding simple concepts when necessary. I remember he had an argument about high-quality photos of the earth seen from space distributed by NASA. It was based on some evidence that they were composite images. He had some totally clueless argument about no being able to project 2d surfaces (like those of photos) onto 3d surfaces like spheres. I mean, that is a pretty standard thing to do in 3d graphics texturing so I asked him about that and he would just get confused. It would almost be like you couldn't explain why 1 + 1 = 2 to him in those moments. Every step of the argument was drawn out and made excruciating.
I became cynical about it eventually. He was reasonably intelligent on almost any subject. I figured he just liked being a Socratic debater type, in the sense that he just loved to push people into corners of science they didn't quite know and prove to them that their own beliefs weren't as solidly founded as they thought. Once I realized that I just stopped any debate on the topic immediately after it started.