I understood the terms as follows:
* contributor: an individual who takes action to shape the the repository / project. in nostr-of-git-world this translates to sending patches, issues, or comments / replies to a repository.
* maintainer: an individual who has the rights to push commits to master branch of repository available via the git servers listed in the 'clone' field of the event.
clearly this isn't a shared ontology 🤣