The author cannot do math. In a population of about 2M, if "hundreds of thousands" had fled, the drop in Serbian population percentage would have been much greater than 13 percent.
Over a 27 year period, a significant differential in birth rate can also make a big difference in population percentage.
The author actually is correct. The "64% to 77%" rise was between 1953 and 1980. The "hundreds of thousands of Serbs and other non-Albanians had fled" was between 1980 and 1996. Kosovo is now about 97% Albanian.
Here are some articles from Western newspapers re the exodus of Serbs from Kosovo from the 1980’s, before the anti-Serb propaganda started: http://emperor.vwh.net/articles/benworks/1980news.html#BM9
Have you ever heard of a term called “birth”? :P
Think that through...
the numbers are close to correct.