Since then, Supercell hasn't commented publicly about creating a separate server for players in China until recently which I just found in the Supercell Support website. I'm excerpting and bolding a portion for emphasis.
Can I transfer my game account I downloaded outside of China?
Unfortunately, no. Transferring your account data from the international version of Brawl Stars to one of the official Chinese Brawl Stars versions is not possible. In order to maintain compliance with the Chinese government's regulations, we have developed a separate version of Brawl Stars specifically for China. Top reasons to download the Chinese version include access to Chinese servers, providing you with the best possible latencies during battles. It also offers the only way to purchase in-game content.
Playing the Chinese version will also enable you to easily link up and play with your friends using popular Chinese social networks! As the Chinese Brawl Stars game servers are separate from the international servers, account data cannot be shared across regions- adding to the difficulties in transferring accounts across regions.
Now we have confirmation that two Supercell game teams created a separate server for players in China after releasing an update. I'm speculating the following. If many players in China are playing Hay Day on Android devices, then Team Hay Day will create a separate server for them to continue playing. If there aren't enough players in China, Team Hay Day will deny them access to the game.