Don't know how they came to this conclusion, if you look at the headers of https...

Don't know how they came to this conclusion, if you look at the headers of https://twitter.com its listed as "tfe".

  $ curl -v https://twitter.com
  [..ssl handshake and request..]
  < HTTP/1.1 200 OK
  < content-type: text/html;charset=utf-8
  < date: Fri, 01 Nov 2013 11:12:31 GMT
  * Server tfe is not blacklisted
  < server: tfe
  [..body..]

Also interesting to note that they are identifying sites such as "github.com", "dell.com" and "starbucks.com" as all using GWS[1].

[1] http://trends.builtwith.com/websitelist/Google-Web-Server