It's an example how to have a desktop shell client for Weston, based on a real toolkit.
The idea is that this client, or any other based on any toolkit, can interchangeably be used with a single desktop plugin like the weston desktop plugin. Therefore, one compositor, with a single desktop plugin can be used as a foundation for building different shell UIs based on different graphics toolkits.
You are free to get this code and use to build real GTK+ shell clients as you wish. All you have to do is add the MIT license on your project, maintaining the copyright in there.