According to who? Are we just redefining terms now?

The economist wants to predict human behavior. This being the case, the economist is only interested in values that someone actually acts on. The 'best' utility function for an economist is the one that completely predicts all actions of the agent in interest. Capturing the agent's true values is subservient to predicting actions.

The ethicist wants to come up with the proper course of action, and thus doesn't care about prediction.

The difference between the two is the two is normativity. Human psychology is complicated. Buried deep inside is some set of values that we truly want to maximize. When it comes to every day actions, this set of values need not be relevant for predicting our actual behavior.