With WebRTC the "without any server infrastructure" only refers to the P2P part. The session initiation is outside of this. So in practice this means you need a server for the initial handshakes and then the actual session is P2P.

Running over WebRTC the web browser based person can communicate with the host person who is running a native WebRTC app.

The session initialization needs some kind of middle man (server) that lets both parties to agree on the session communication details. This per se doesn't really need any account.

The person who wants to host the session could generate a temporary one time auth token that they then communicate to their peer using whatever means (send a pigeon, use email, chat app) that lets the client to connect to their host.