Keep in mind that this article talks about directly measuring the pH of the meat itself, rather than the pH of the 'ash' once the meat has been metabolized. When people say "meat is acidic", they really mean to say "the metabolized ash of meat is acidic".
For example, a citrus fruit is acidic (tastes sour in your mouth), but its 'ash' (after metabolization) is alkaline, so people say that "citrus fruits are alkalizing".