Page Authority is simply used to discover the ranking of your website when tested with the algorithm set for it. Page Authority is tested through the data extracted from the data on Mozscapes Web Index and the number of links that can be counted on the website as well as those from MozRank and MozTrust as well as numerous factors, which are more than 40 in number.
One thing to note is that Page Authority (DA PA Checker) is not focused and would never use such things as the number of keywords used or even the optimization made on the content.
Read more at: https://moz.com/learn/seo/page-authority
