> the real question is understanding why he is inclined to believe its a hoax, rather than trying to pile up evidence in front of him

This is one of the primary techniques of SE. People are open to answering questions and with some skill with Socratic questioning, you can get results. Dumping data just causes cult/hoax members to feel threatened because you're attacking some core beliefs and they will try very hard to avoid losing a sense of self value[0].

Notes:

0 - "What I believe is wrong" -> "I am wrong" -> "I am a bad person".