The difference to YouTube is that it's not intended to create a huge platform centralizing videos from the whole world on a single server farm (which is horribly expensive).
The web browser generates a random string to identify the viewer during the browser session and periodically notifies the server that a user is watching the video.
This means that anyone can download and install PeerTube to host videos on a specific domain name (this is called "hosting a PeerTube platform/website").