The official fertility rates for that period was 1.3. For reference: 2.1 is the replacement rate.
If anything their total population went down during one child policy.
Even if I take your numbers at face value, it is absolutely possible for this math to math. To simplify massively, if the average person dies at 80 years old, the population growth today depends on the number of births 80 years ago, compared to today. Not 30 years ago. The population may have grown massively between 30 and 80 years ago, so that the absolute number of births remains high, despite a low birth rate.
And this fits for China where the standard of living has massively increased. What would throw off most Americans is that in 1962 the average life expectancy in China was only 50 years old, and has increased to roughly 78 today. 28 additional years of life is huge and it was so rapid that it would create a massive increase in population.
This also reverses causality on the one child population rule. They didn't add the rule because their population was huge at the time, it was added because increased life expectancy with nothing else would have increased their population now to something like 1.7 to 2 billion.
Different population distributions. In particular, the population of China is concentrated in the eastern half of the country, with very few people living in the western half. Contrast to Europe, which from what I understand is more evenly spread out.
Imagine this scenario: tomorrow the Ukrainian front collapses, and Russia rapidly captures a significant part of Ukraine. Then the Ukrainian government gets Venezuellaed by Putin (maybe with Trump's help), and the new government becomes loyal to Moscow.
Then a new charismatic military leader deposes Putin and forms an alliance with the Ukrainian army against Europe. With rhetoric like: "Look, Europe just used you. They never gave you enough weapons to win against Russia but just enough for a stalemate. They were giving Putin hundreds of billions for gas and oil, too afraid of cold weather while you were dying on the front lines. They hoped to kill both of our countries. Now let's join together and show them how the war should be fought properly". And then a battle-hardened 500000-strong army marches towards Kaliningrad, locking Poland and the Baltics behind the front lines.
It's an exceedingly unlikely scenario. But not impossible. And it's not the _only_ similar scenario anymore. There's also Turkey with a dictator dreaming about writing his name in history books. Serbia is getting more anti-EU.