Ya, you basically interpreted it correctly.
Though mangos is under GPL and can be retrieved for free, however, there are large portion of Chinese could not read or not proficient in English, Most of them dont even know how to use git to get mangos, from there, mgcore just took that advantage to provide Chinese copy and gain profit. Further more, Chinese client is a bit different from enUS and Europe version, it has been altered by agent to add more security measures, so, pure mangos cant be used for chinese version to connect, some modification has to be done. Most ppl simply dont have sufficient knowledge to do that.