Humans have been storing food for winter for hundreds of thousands of years before agriculture and the invention of writing, you think they all died off or something? People whose crops failed instead were more heavily affected in winter than hunter gatherers.
No, people starved way more with farming than with hunting and gathering. All in all you're under very severe misconceptions as to how farmers and hunter gatherers lived which is not supported by the evidence.
That study controls only for habitat quality, which I feel is not really relevant: hunter-gatherers are, by definition alone, nomadic. They move to where the food is!
IOW, hunter-gatherers follow the best habitat, so controlling for habitat is always going to have the conclusion this paper reached.
I'd be very interested in other studies that support this conclusion; after all, that's how science works - a single study proves nothing if many studies conclude the opposite.