[China may still want to start a war with a pushover, in part to cull their own surplus males.]
Its unclear to me which great thinker first pulled this particular theory out of thin air, but nobody sends soldiers off to war for the reason you cited. China is far higher income (2x-4x) than many of the countries to the south and west, and could import millions of picture brides to fill the need if necessary. But the reality is that Japan and Korea have far higher numbers of unattached males and theyre not exactly revolting. War as a means of dealing with internal pressures is fine if the outcome is more or less guaranteed and the casualty numbers are likely to be low. That does not describe any war in which the US is Chinas opposite number.
Major Chinese dynasties have fallen with the entire royal clan, numbering in the tens of thousands, killed to the last man, woman and child, in the wake of major battlefield defeats. Chinese policymakers dont always make great decisions, but they always consult the past.
Thanks Zhang Fei.