Many trademark holders have a policy that you can't use their name as the <i>prefix</i> of the name of something else. So e.g. JavaCache would not be allowed but Cache4Java would be. This reserves the prefix for official products which in theory reduces potential consumer confusion which in theory is the purpose of trademarks.<p>And a name like docker-marklogic is double doomed because both parts are trademarks so you probably can't say marklogic-docker either.
The title is misleading, IMO. Looking at the image of the mail conversation, it looks like the author of the repo initiated a mail with docker legal team asking if it's OK to use those names to which the docker team politely replied it isn't allowed and also explained why. The author of the repo then goes on twitter and curses them. Don't see docker doing anything wrong here.