I distintively recall back when I was joking about getting popcorn ready and Overborn stated he would buy an NFT, that he also said the hint is to look at what the Chinese embassay does, many other countries were already telling their citizens to leave and offering evac (this was pre-invasion) but China had not yet taken action, Overborn surmised that once/if China took action that was 100% certain the invasion was going to happen....
So surely many other countries and actors/players were also looking for hints and anything that would tip them off
I'm inclined to believe China did this for OPSEC and like the Vulcans often say, the good of the many outweight the needs of the few. The fact of the matter is, entire fate of civilizations are at stake and often it hindges on criticial moments such as these, so in the grand scheme of things sacrificing the safety of some Chinese dispora abroad the Ukraine in terms of cost benefit analysis may have been determined to be in the best interest of the long arc of Chinese national interest and Sino-Russian relations in order to maintain the element of surprise and timing or whatever it is 4D chess and 11D Go that Putin and Xi have in store that has yet to play out .