Yes, it is quite old — only up-to March 2017. Also, GHTorrent relies on public GitHub events.
“ Github only creates events when an entity is created and not when it is updated or deleted. It is therefore not possible to be completely up-to-date with changes in users (e.g. updated location) and repositories (e.g. renames). GHTorrent tries its best to stay up to date by refreshing all users and all repos every X months. As the DB contains 12M+ users and 30M+ repos, this process may take a while and it can also fail due to spurious reasons. ” — http://ghtorrent.org/faq.html
This simply means that if someone unfollows you in GitHub the record will still remain in GHTorrent. It will still count as a follow if we query from GHTorrent. The best way to get the latest and correct data is to do what you did, use the GitHub API.
If we happen to use the current GHTorrent database, it will still have some misreadings.