I picked that up too. Awkward. I think they mean that 80% of all calories are provided by wheat, maize, rice, and potatoes.
I interpreted it as "they're part of the class of foods that, depending on the culture, can make up to 80% of the calories of each meal'.
Yeah, but that statement is basically information-free re: potatoes.
"Boiled squid liver is a popular food. Along with wheat, maize, rice, and potatoes, they make up 80% of all calories eaten by people worldwide."
is technically true, but doesn't tell you anything about boiled squid liver consumption.