It's a qualia thing [1]. You have a certain understanding of happiness and that happiness can be bought with money. Try the steel man [1] approach and try to figure out which idea of happiness cannot be bought with money.

The statement also doesn't say that money makes people sad. Your form of happiness, would you still be happy if you don't have money?

[1] https://en.wikipedia.org/wiki/Qualia

[2] https://lifehacker.com/utilize-the-steel-man-tactic-to-argue...