I didn’t know that (at least, not explicitly). So, not really generous at all? Also, buffers; another reason for Mao to not take it would be to have a buffer with Stalin. Buffers, totally a reason that it is better for China to have Japan, Korea, and the Phils in their sphere of influence rather than have those as US allies without much in the way of buffers (to be fair, on land there is NK).
Another good one from the Economist, of course perfect analogies are difficult, so
Any more than comparisons with WW2 do. But it is worth considering history when we try to see the future.