He told me to save some money and invest it. I gave him nothing and have more money in the bank. How does this make me foolish?

His message is basically summarized as "Spend less than you earn, and invest it in index funds."

He's not wrong, but I submit that the people implementing that advice aren't fools, either.

I'm referring to his comment about starting a cult. He is right of course that finding gullible people to follow you is easy. Just say some obvious things like "don't spend all your money, save and invest!" and the sheep will flock. Maybe you gave him no money, but you spent your time and attention.