I can easily forgive the statement you highlighted, but there is zero information about potatoes in this one:
Along with wheat, maize and rice, they are estimated to account for up to 80% of all calories eaten by people worldwide.
The point is that potatoes are one of the top 4 food sources worldwide, and they collectively dwarf the percentages of the long tail of other food sources.
Proportions vary significantly continent-to-continent and culture-to-culture, such that it'd be more meaningless to try and put a more precise (but less accurate) number on it.
This is not difficult to parse out of the sentence if you choose to take a charitable rather than a pedantic perspective, which I recommend to you generally.
I picked that up too. Awkward. I think they mean that 80% of all calories are provided by wheat, maize, rice, and potatoes.