It appears they are just using an alternative phrasing without making comment, but if they were actually making a comment then wouldn’t the overall objection be “not to read too much into the wording”, but that is a catch 22. Objecting to someone taking wording too seriously to the point of changing the wording is in itself taking the wording too seriously.
Not a native speaker (never heard "clear box" as terminus technicus), but a mathematician: If it is "the (only) opposite", the relation ist symmetric. So the opposite of "clear box" is "black box" again. Skipping the injective part, "black box" would be still one possible opposite.
No, it makes no sense to change a well-known phrase to an unfamiliar and goofy sounding one just to appease a silly ideology that injects racism into everything.
> It has nothing to do with racism, but good on you for bringing racism into the argument though.
Nonsense. This is all part of the "oppressive language" concept peddled by the neo-Marxist authoritarian types.
> Some people use the term opaque box instead because it a more clear antonym to clear/open box.
This is the first time in my life that I head the term "opaque box" used instead of "black box" in this context. I couldn't even find this phrase using a Google search.