Weird. Fake? Bug? Whatever it is, I dont think that is accurate at all. Thanks for sharing it though.
Pretty sure it's some coding mistake when they created the script. Maybe they though a PR 10 could not be achieved, so they put it "if PR10 then NOT VALID". Weird though.
Websites like Google.com, Facebook.com, Twitter.com, etc achieved it to become PR10 for sure so it must be a coding issue or maybe they went above PR10 .
Actually, Google and Facebook are PR9, and Twitter is the only PR10. That's the weird part. Maybe they are pointing out that there can't be a site which has a higher PR than Google, thus labeling it as a fake.