It would be helpful to write out the argument, since it is very hard to follow in the first place and has questionable assumptions right out of the gate. There is absolutely no evidence that hibernation is an ancestral characteristic in the hominid line. Or that pre-hominids in our line (Plesiadapis for example) were adapted to cold weather. You pretty much have to have no education whatsoever on primate evolution to even accept his starting points. The only known primate that hibernates does so at tropical temperatures.

And if his theory panned out, diabetes would be more common in polar cultures, particularly those in which neolithic diets have been introduced. But if you look at the data on Siberians (Leonard et al.) that is not the case at all.

And the vast amount of evidence shows that cold weather adaptations are derived, IE pretty recently evolved, and not ancestral to the homo sapiens species. That's why they are so poorly distributed. In fact, they might even be relics of interbreeding with sub-species like Denisovans and Neanderthals.

And if diabetes were an evolutionary relic, why is there so much evidence that it has to do with autoimmunity?