That is for a fact not true. I happened to have worked on many titles on this website as a proofreader. I assure you that almost all of the raws listed on mangago were scans taken from Cantonese/Taiwanese sources, whereas the original raws used by the scanlation groups are almost always original Japanese, purchased by a third-party scanlator, the scans of which are never disclosed on the internet unless requested in private mail by another group for clean and retranslating. You can especially tell if a group is working with chinese rescanlation because a lot of the sound effects will be left in Chinese - the vast majority of scanlations in English on this website, I assure you, came from Japanese.
I think they are just using it as a generic term more than anything, and not meant to be prejudiced. It's like they want people to understand (on English sites) that no matter what language the scan was taken from (as I have seen a few - very few - in Spanish) it is not a translated and cleaned English version. Sort of like labeling all crunchy sweet baked goods as cookies - yum...cookies, oops I guess I should not have used that example - but it was the best I could come up with - and now I have to run and get a couple of cookies! Darned imagination.
The raw refers to an original of the manga. It doesn't matter if it's Japanese or Chinese as long as it's a copy from the actual manga and not a set of images that have already been worked on. There are also manga that are made originally in Chinese not Japanese as well as Korean manhwa. Raw is also a scanlators term that just happens to be used by others so it comes off incredibly rude and pompous to attempt to lecture others on it's use.
Am I the only one that finds it a bit incorrect that raws are this website are mostly Chinese. Maybe it's because I speak Japanese, but I find it very annoying that "raws," which are supposed to be the literal, untouched, original copy of the manga in the language of origin, are simply treated on this site as though the term refers to any form of the manga that is in a language that isn't English (most commonly and language that looks vaguely Asian).