Grouping of food items into various classes is a very old idea of Ancient Greek, Alchemists & Ancient Indian School of Medicine (Aryuveda). These ideas are perhaps thousands of years old. From a scientific perspective these classifications don't mean anything today. For example, in those schools of thought, fish has a very "hot" effect on the body but yogurt is "cold". Similarly, citrus fruits are "cold" but dried dates are "hot". Now nobody can define what hot or cold means and what is the criterion?
Similarly, the chart shown in the original posts are all wrong. It is just a modern version of these ancient schools of medicine. I think the major source of confusion in calling limes and lemons is that citrates (salt of citric acid) are indeed alkaline. Many antacid concoctions use solid sodium bicarbonate and citric acid. The moment you add a spoon to water, it starts to fizz vigorously. The pH of such solutions are slightly alkaline. Perhaps whoever made those charts had these ideas in mind.