I've looked at many charts with lists of acid/alkaline foods, and they all seem very confusing. There are so many out there and not all agree. I expect what I personally need is a guide to food on both sides of the pH range. This one with the introductory explanation seems to be the most helpful one I've come across.
EDIT: I think the key statement in this readout is "it depends on the mineral content of each of these foods". That would be determined by the nature of the foods and how many of the minerals were available in the soil the plants were grown in, which seems to be the variable, since our soils are depleted of many of the necessary minerals now.
No one knows about the quality of food that was used to determine this or where it was grown, and it might be what might makes things so confusing.