To be absolutely honest, I'm not sure if anyone really knows. Meat is sold in stores and it tastes the same as any meat I've had before [Better even.] Personally, I don't believe it comes from non-pokemon animals. You'd see some trace of those out in the wild, but there aren't any as far as I can tell. Which means the meat is either from pokemon that are slaughtered in a particular way that makes the meat edible to humans, in the same way you might have to skin a poisonous creature in a certain way, or, uhm, I'll admit I'm not really very educated about this particular field, but I once talked with someone who said it is possible for scientists to produce meat in laboratories.