I think there are confused definitions for "sustainable."

There's "sustains the land," which is food that can be grown this way indefinitely, which is what most people mean when they say "sustainable agriculture." To be more specific, "meeting society's present food and textile needs, without compromising the ability for current or future generations to meet their needs."

You're saying sustainable as in "can sustain the future diets of 10 billion people."

They don't map 1:1.

TBH I think you're right. "Sustainable agriculture" isn't scalable to 2050 populations.