“Gay” used to just mean “happy” in English. Now it doesn’t. Language is fluid.
Gay still means happy in addition to now more common informal use for homosexual person.
Moron was originally defined as a psychology term for “a person of mild mental retardation” in certain IQ range. While the new informal meaning doesn’t relate to the technical term in psychology, it still means stupid person nevertheless.
Context matters.
The context of the use of “moron” in that post was an insult. And there is a clear definition as to what moron means in that context.