As stated, this is 5 years earlier than last projected, due to the effects of the pandemic. The US is not going to like being in the number two spot, and even less when India’s economy then surpasses the US after that. The biggest benefit to this massive Asian economies is the sheer number of people. The United States’ best hope of competing is to increase the number of Americans and, and quickly.
So how the USA is going to do that? Do you think they should let foreign people come to their country and govt should give them lands and money to build a firm? People in the western county is not like Asian. Most of the people in western countries do not like to have many children or do can not produce more because they are so busy with other things. Also, most of the people do not like to leave their own country if they are not in need. If Asian people can produce enough money to make an easy life they will not go to western countries no matter how big their salary is.
I would say the joke was about having a lot more kids for the next generation and not just getting more people. Obviously having kids will not help you in the next 8 years, but it was a joke after all. If it was just a joke, I would say it was simply just a logical argument where having more people in your nation would mean you could make a lot more money with a lot more work as well.
However USA is doing fine what they are doing right now, they do not need to be "biggest economy in the world" to be a powerful nation, do you know why? China will be big, but it will be big by CCP, all those Chinese horrible disgusting officials will be rich while regular people will be poor, USA could still have poor people but even working minimum wage in mcdonalds will give you 10x better life than a regular Chinese.