Yemen is split between political factions such as the contemporary president attempting to establish a government in the south and the Houthi leadership who have used military force to take control in the north.
China and Russia are speaking out about the fact that some of Iran’s and Yemen’s military supplies warehouses were struck in addition to the official non-state-sponsored™ “rebels” controlled sites.
So while China is right in saying the USA and UK backed by several other nations attacked a non-hostile nation, it’s also clearly posturing and ignorance of the facts that those target sites were weapons actively being used against them or otherwise against other innocents including potentially their own peoples.