This assumes humans could turn 100% of the feed into usable calories. Considering 1) the link defines feed to include grazing and 2) humans are 0% efficient at turning cellulose into calories, the quoted number probably doesn't mean what you think it means.
Even if you’re just talking about biological calories rather than as a unit of energy, fire reduces energy expenditure to stay warm. Thus acting as a significant food supplement both historically and currently.
This is still a bit of a stretch to make a relevant point given the context of the discussion. I don’t think many are promoting getting rid of cattle to make room for biomass fuel.
I've seen that argument made several times. EV's are great on land, boats have several options, but for mid to long range air travel biofules have a lot going for them. Unfortunately they need a lot of land.
The underlying numbers seem reasonable with US airlines use ~10 billion gallons of fuel per year while the US produces ~15 billion gallons of ethanol being freed up by the rise in EV's.
Globally things aren't as rosy, but freeing even 1/5 of the land devoted to grazing, alfalfa, and feed corn would go a long way. Reducing US beef consumption would have positive health impacts. So from a policy standpoint shifting the specific subsides seems like a good idea.
Even if we can't get net zero the more we can cut quickly the longer we have to finish the job.
US produces about 27 billion pounds of beef, roughly half of that weight comes from feedlots where they eat ~80% of feedlot calories comes from grains.
There's a bunch of numbers tossed around but it's something like 60-70 billion pounds of grain to get those 27 billion pounds of beef.