The devil is in the details, e.g. people usually self report very different levels of happiness if you ask them more or less frequently, and if you ask them about general happiness or in the moment happiness.

Also someone if someone told you they couldn’t make you happier but they could make you more comfortable, more healthy, or more secure, that’s still a life improvement, so it’s possible it’s linked to other positive life outcomes. Happiness quite literally isn’t everything.

Also, when someone is unhappy they will usually report that accurately, but when people are not unhappy they often fail to report themselves as happy or even just not unhappy, when perhaps they should, because they normalise to it and so on. We’re just bad at reporting this stuff.