He has a very thought out method for determining who to listen to, it's a method known as confirmation bias. If someone says something he already thinks, they must be trustworthy.
Pretty much summed up in this Wiki page:
https://wiki.tfes.org/Place_of_the_Conspiracy_in_FETP1) If personally unverifiable evidence contradicts an obvious truth then the evidence is fabricated
P2) The Flat Earth is an obvious truth
So even though P2 is not backed up by any evidence, just declared to be true, they can dismiss the tsunami of evidence showing it to be wrong.
So there has been no actual response to Elon Musk's launch, no evidence that it was faked, for example.
But if the earth is flat and space travel must therefore be faked (not quite sure how those two things are connected, even if the earth were flat surely we could still develop the technology to leave it, but given that all space travel shows a globe earth it's declared to be fake) so the launch must have been faked somehow.
It's easy to prove oneself right about anything if one dismisses all the evidence showing one is wrong.