That last one about tuber paste being butter is actually wrong! Grubloaf is supposed to be "meat" like meatloaf and tuber paste is a reference to potatoes (also known as tubers) as in mashed potatoes. So what he's saying is that it's the "meat and potatoes" which is a pretty basic term for something very basic and common, the base of a thing.

Gotcha! Sorry I thought he was saying something akin to “bread and butter”. I’ll change it.