That is indeed the only reference I could find (and maybe Cue is inspired by this paper?), but they don't seem to explain why they use such language. They talk about "unjustified reasoning" and laws, but the connection to ethics seems questionable. But I've not read the whole paper.
A moral equivalence class is an axiomatic equivalence class that when quotienting some mathematical structure the model in question might lose some of its soundness or adequacy properties, but one that nevertheless might be useful for other meta-mathematic reason.
This use of the word is so common in certain math/category theory/compsci communities that I was not aware it was unconventional in any way. It has nothing to do with ethics.
I guess the moral of the story is that the moral of the story can be lost if people don't understand the story.
