This comment would be more useful if you said what browser you were on when you received that error.
R = window.RTCPeerConnection || window.mozRTCPeerConnection || window.webkitRTCPeerConnection || window.msRTCPeerConnection;
U = window.RTCSessionDescription || window.mozRTCSessionDescription || window.webkitRTCSessionDescription || ["window.msRTCSessionDescription"];
R && U || (w.style.display = "none",
I'm betting browsers (or at least FF) make it deliberately hard to tell if the browser is in a "has WebRTC capability but it's disabled" state (to avoid fingerprinting), so I don't really place the blame on the author.
Disabling WebRTC is something that was deliberately done, so that's on you to remember that you turned it off. Sure, the message could be more helpful and say "this website requires WebRTC to function", but a browser with WebRTC turned off is in fact not supported by this service.
(Firefox, with WebRTC disabled)