They're omitting the fact, that a lot of the biomass we're eating comes from farming. Those plants that collect carbon dioxide from the atmosphere use a lot of synthetic fertilizers to grow, which itself uses A LOT of fossil energy to be produced.
The CO2 emissions per calorie of food varies almost 3 whole orders of magnitude between different food types:
https://ourworldindata.org/grapher/ghg-kcal-poore
At the same time, our CO2 exhalation is about the same per calorie of food, regardless of source. So it's more fair to describe our baseline biological needs and bodily functions separately from our economic consumption of the products we prefer to consume (food or otherwise).
So I still think the focus on the raw calorie count of our consumption (and the accompanying CO2 exhalation) obscures, rather than explains, how our food consumption contributes to climate change.
That's why I'm skeptical of degrowth actually doing something to effectively reduce consumption. Because some individuals consume 3, maybe 4 orders of magnitude more resources (and the accompanying pollution or ecological destruction, however you want to measure it), I've always believed that reducing population runs a significant risk that the remaining smaller population will use far more resources than the previous larger population.
You see it in rich countries. We have low birth rates and high consumption rates, and our consumption grows exponentially even as our population does not. We run a serious risk of being very destructive childless retirees, and consumption and pollution and emissions and ecological impact need to still be worked on, even if we do shrink the population.