They did.

We make enough food to feed 10-12B people

If we feed 8B but could feed 12B if we didn't eat animals, that's 12-8=4, 4B more people, and 4/12=1/3, or a third of our crops that could be used to feed people instead of animals. Which is right at the percentage of crops used for animal feed, ~36%.

You are correct that they did use the word "most" instead of "much" which wasn't as accurate as their math. I guess I focused more on their concrete descriptor while you went with the fuzzy one.

Either way, the truth is certainly that we could mitigate the crop loss of climate change with a simple alteration of our diet, while we figure out where, when, and how to grow crops now. It likely won't happen, but it's possible.

Unfortunately, just like with the current percentage of the population that is actively starving, the greater percentage in the future will likely just be forced to die, even though they can be easily fed.