The data in your graph is too coarse to show the war dip, but other similar graphs your ML friends always cite, conveniently start right in the middle of the war period.
But regardless of that, your graph clearly shows that the before and after war life expectency was about the same, then there was a significantly delayed improvement during Mao's reign of terror, and when he was sidelined due to illness in the 1970ties and capitalist policies adopted, China finally caught up to its peer counties.
Just compare your graph with the development in South Korea: https://www.statista.com/statistics/1088199/life-expectancy-south-korea-historical/
And you can clearly see that Mao delayed the improvements seen during that time all over the world. And no, I am not claiming SK was a great country during that time, yet somehow despite having a brutal military dictatorship they still outperformed China under Mao on this metric, which shows just how bad Mao did.