It does not require a central server, signaling is left as an implementation detail. Implement a p2p signaling system, and that will be p2p.
Is LAN P2P? If yes, WebRTC is 100% P2P over LAN is it not?
I still think the clients need a coordination server to discover each other (won't use multicast/broadcast traffic). You could probably make a browser that does this, but if they already do then I am not aware of it.