Docker is a software tool. Docker Hub is a service. If Docker didn't stand up Docker Hub the equivalent services from GitHub, Google et al would have competed on a more even playing field.
It's almost like they created intentional ambiguity here when they renamed the company (dotCloud) to match the name of the open source tool, then renamed the open source project behind the tool to something else (Moby), but kept it for the command line tool, while also combining the name Docker into their product offerings, including Engine and Deskop, that handle completely different parts of managing containers. That's not even including registries, dockerfiles, Compose, Swarm, etc. and the ambiguity around where those sit in the a Venn diagram.
