A Vision of God from Faith in Our Knowledge

Hello Rabbi,
In lesson 20/21 of Faith and Its Meaning, the Rabbi explains that if someone gives confidence in their epistemology, then they necessarily also believe, but of course they can also not believe in both.
Can’t we argue more strongly that if an atheist even argues with me about this issue, it means that he actually believes? In other words, if he doesn’t give a damn about anything, then maybe we don’t exist at all and everything is imagination, etc., and there’s no room for this debate at all.
I hope I explained myself well.