They could be giving out different IP (or CNAME) for people using their DNS. Then the site is just slightly different depending on how it is accessed. or i suppose they could be looking at logs of the ips using their dns and checking all visitors to the website, but that would be wild.

ooh they could also have a host that is only resolvable from those servers, and have the front end dynamically load that message from that host. and if it fails it does not show anything.