It’s correct in the long run and can be incorrect in the short run (and, indeed, is incorrect at this particular moment in history).

It's correct in the short run, incorrect in the long run, and correct in the ludicrously (I'm talking cosmological scales here) long run. For all practical purposes, the long-term is much less zero-sum than the short-term.

Human existence has only been non-zero sum globally for the last hundred years or so. Additionally, it’s been non-zero sum in the Americas for several hundred years before that, but only because all the natives were wiped out. The rest of human history has been a zero sum struggle for existence.