The main question for a site like this is: how are you collecting your data? CDNs have dozens of nodes and the performance a user sees will depend on what the network looks like between them and the nearest one. For example, if all your measurements were from an EC2 instance in us-east you'd only be measuring a tiny and easily-gamed slice of CDN performance.
On their about page they write that they're "grateful to Pingdom for providing access to their data" but I can't find anything more about which and how many places they're measuring from or how they combine measurements from different places.
Disclaimer: I work for Google on mod_pagespeed and ngx_pagespeed, and I sit near the people who handle developers.google.com/speed/libraries/ But I don't know anything about how they serve the hosted library traffic.