You can't have complete peer-to-peer with browsers unless you properly implement multicast groups or something of that sort. So peer-to-peer needs help bootstrapping by providing some registration service (a meet-in-the middle if you wish).

That is what Telefonica might be doing -- providing a default registration service.

Also because of funky routers and NAT rules, even after the initial session is set up data/audio might not be going through, so then you need STUN or TURN servers so Telefonica might be providing those as well.