How exactly is docker (buildkit, compose, the runtime, the daemon, etc) not open source? Docker desktop isn't, but that's almost entirely unrelated to the containerization technology that it uses or that people refer to when they talk about docker.
That service agreement is for using the Docker Desktop GUI tool which isn't open source (though free to use for small businesses etc) whereas the basic docker CLI commands are all open source.
https://i.imgur.com/2F0JmUw.png