That statement can mean pretty much whatever you want if you carefully choose your definitions of "sustainable", "overpopulation" or even "meat". I wouldn't go as far as to tinker with the definition of "Eating", but could tamper with the implicit size of the daily ration, which is almost as good.
In conventional terms, though, no. You cannot expect to have 7+ billion people to eat as much beef as the average American on a daily basis for any meaningful length of time without causing severe environmental damage.
Maybe the 1 billion at the top of the global economy can, but if this comes at the cost of having the 1 billion at the bottom starve, not because actual lack of food, but because they get priced out of the market by the cattle... I don't see it as an overpopulation problem, but a wealth distribution problem.
Well, yes, the total sustainable population of Earth is down toward 2.5 billion. Nobody said anything about accommodating 7 billion as sensible policy.
You are correct about that, maybe even in the upper limit.
Given that you are aware of that, it makes even less sense to pretend that 1 billion people can keep eating the amounts of meat that are currently considered "normal" in the US.
Some people can eat that much, or even more. Those people probably live in an environment where the land cannot produce that much vegetable calories that are eatable by humans, but do produce the low grade, cellulose rich stuff that was typically used to sustain cattle.
In different geographies, where grain can be grown in big quantities, people would be better off eating the grain rather than feeding the grain to animals and then eating the animals. Meat can still be raised in that environment, as a complement, but probably not in the amounts we have gotten used to.
In conventional terms, though, no. You cannot expect to have 7+ billion people to eat as much beef as the average American on a daily basis for any meaningful length of time without causing severe environmental damage.
Maybe the 1 billion at the top of the global economy can, but if this comes at the cost of having the 1 billion at the bottom starve, not because actual lack of food, but because they get priced out of the market by the cattle... I don't see it as an overpopulation problem, but a wealth distribution problem.