Eliezer knows aliens are real and will be disclosed soon. He's rallying people to dump money into a bet he is secretly betting against to teach them about the fallacy of appeal to authority.
Other
UFOs are a product of a massive conspiracy unrelated to non-human entities
Ultraterrestrials (home-grown, advanced non-human civs, hidden from us)
UFOs are part of/directed by a superintelligence
AI is harder than practical interstellar travel
UFOs are aliens intentionally both hiding themselves and revealing themselves to sow chaos
