Ah. Is that it? I'm french, so monocoque means 1 piece, pretty literally. One piece monocoque then becomes monocoque moncoque, or one piece one piece, which sounds redundant if not retarded.
mono-coque. one-shell. If you glue 2 pieces together i dont see how it's any more 1 shell than if you weld lugs and tubes together, but i guess here we are.
And from my various discussions with chinese sellers, when the topic of monocoque comes up, it's to say that they use one mould, not 2, that the tooling costs more, that it's more premium, lalala. It is possible that they mean / imply one piece monocoque, because they speak chinese to begin with so idk how they translate the nuance, but saying a carbon frame is monocoque to mean it's made gluing 2 triangles is like saying a carbon frame is made with carbon fiber. Or that walnuts are vegan, the sun is hot, and water wet.
I think some Chinese sellers are trying to communicate with you what the product is and work around the misunderstood terms. They are just trying to do a good job helping you understand why a product costs more. If you use the word "monocoque," they probably will just use it to get through the conversation. The language barrier is real, and there are three languages to work with here: English, Chinese, and Western engineering speak.
There are also still a few modern non-monocoque carbon road frames out there. The Enve Custom Road and the Colnago C68 are additional examples.
I normally wouldn't bother to engage with this misuse of terms, except that it's now being used to evaluate whether a frame is worth buying, rather than just describing something esoteric. Once we move that language into common discussion, ensuring that it actually means something is important. Because "monocoque" refers to how loads are supported, there is likely to be a difference in ride feel between how a monocoque and a non-monocoque frame that are otherwise visually identical. On the other side, the consequence of having a frame molded in one piece vs. 2 bonded together is likely just a tradeoff of less weight vs. lower cost as the loads are supported the same way, its just glued together slightly differently.
In other words, the real issue with this frame moving to a separate rear triangle mold is a few grams, which is probably not much to worry about for an aero frame like this.
As to the person who confusingly coined the term. IDK, he was some French guy. Just don't google "is water wet" and blame me for the result.