There are two seperate things here: 1) KNOWING right from wrong and 2) being able to explain the logic behind it. Someone can know intuitively what a car is but not be able articulate and explain just what makes this thing (a smart car) a car as opposed to a golf cart with a roof.
Hashem has imbued each person with the intuition- with regards to certain things- as to what is RIGHT and what is WRONG. Ask a secular person if an incestous marriage is wrong. They will all, to a person, say it is absolutely wrong. Ask them to explain why it’s wrong and they can not. Same goes for having relations with an animal, eating human flesh (from someone who died naturally), etc.
This ability to judge right from wrong is the basis for why and how Hashem can hold people accountable for the evil they do and has been the basis of establishing societal norms since the beginning of time. Adam didn’t have the Torah. Avraham, Yitzchak and Yaakov didn’t either. Neither did any people before Matan Torah. There was still RIGHT and
WRONG.
Therefore when goyim behave in a “WRONG” way, even if one cannot explain logically as to WHY what he is doing is wrong, you can still know that he did do wrong- even according to him.
This is the greatness of all people. The ability to be able to discern and therefore be bocher between right and wrong. To be able to explain your decisions logically to everyone in a way that can hold up to an amoral mindset- that is not guaranteed or required to be able to do the right thing which goyim also have the ability to do.