Wikipedia explains this quite well.
The US figures include coastal and territorial waters. The Chinese figures exclude them. This is supposedly because it’s impossiblebto know what water area is claimed by China.
However, China clearly has a greater land mass area; and measurements including accepted water area for China are bigger than the US including its waters.
I was active - and I mean ACTIVE - on reddit for well over a decade. When the API fiasco happened, I deleted my mobile apps, and stuck to desktop. When ‘opt out of selling your data’ became impossible, I logged out for good.
Lemmy is both better and worse than reddit ever was. It will likely never reach the same activity level, but will also not reach the same toxicity.