Advances in modern medicine had virtually no impact in China's life expectancy at the end of WWII because the vast majority of Chinese did not have any access to medicine whatsoever at that time. They didn't even have vaccines, which had been around long before WWII. They often didn't even have food, with famines being incredibly common before the communists came to power.

Medicine did have an effect later, around 1968, but it wasn't because of a breakthrough in technology but rather because of the wildly successful Barefoot Doctors program, which brought basic healthcare to hundreds of millions of Chinese. The post WWII bump was more because of land reform and lifting the boots of the landlords off the peasants necks, allowing them to keep more of what they growed.

The immediate bump after WWII isn't the main point of the meme, however. The main point is a clear long term trend of rapid growth following a long period of stagnation, with the pivotal turning point being exactly when the CPC came to power.