He’s right but Captain Kirk tumbled to it before him on Star Trek:
What’s there to do about lying liars who lie about their own lying?
Analytical philosopher Richard Johns’s recent paper in an analytical philosophy journal susses out the fact that if any such liars exist, then the lying part of them must be non-physical. That is, he offers an argument against physicalism, the popular philosophy that only physical things exist and that therefore, if humans exist, we are merely physical.
His argument is deeper version of Captain Kirk’s scheme to defeat enemy robots in I, Mudd, a 1967 episode of Star Trek. Kirk posed a paradox that led to circuit meltdown.Eric Holloway, “A philosopher explains why thinking matter is impossible” at Mind Matters News