I think this is giving him too much credit. The sky is a physical thing that you can see (or not), and directly observe. In this regard, anyone that wasn’t mentally ill would question their eyes or their sanity.
In this case, this is just following the same patterns as other pseudoscientists - from anti-vaxxers to flat earthers. If you pay attention there is enough evidence in his replies to show he really does know he’s wrong on most of the information and facts. It’s the creationist tactic of just changing the subject or asking another question most of the time that’s so consistent in avoiding the fevers sting facts that it can’t be by coincidence.
Its interesting watching someone dodge and ignore key facts that disprove them, only to bring up some other unrelated point, or tenuous argument. I mean, Einstein’s been proven, and there are multiple experiments to validate it: any scientifically minded individual would crash headfirst into those experiments like a charging rhinoceros - explaining which part is right or wrong, why - why the experiment does show what they think it does, etc.
Pseudoscientists often cant do that - because the experiments are valid, so they go straight for the famous journal of YouTube, or random internet huxters, as if a plywood interferometer is more reliable than the analysis and investigation conducted. You don’t consistently evade things like this repeatedly and consistently without knowing that they’re increasingly strong.
Conspiracy theorists like this are mostly dishonest and distorting, some are far more ignorant and lacking in intelligence than others, but they all seem to draw some element of self worth, or meaning from the conspiracy, as if “being in the know” makes them feel more powerful.