Twitter using Google Web Server?

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

We've excluded most websites which contain user generated content because of the false positives they give off like this. We've added twitter.com to that list.