You can hover over Community's username in the vote to close listing to find out why it voted:
This question's author approved a pending duplicate vote.
This happens because of this feature:
When a question has close votes as a duplicate, the author is presented with a dialogue to either edit to clarify, or mark their question as a duplicate. By clicking "That solved my problem!", the Community user places a binding close vote and the question is marked a duplicate.
The Community user is shown rather than the author because:
the author doesn't get a binding close vote on their question, so it wouldn't actually be closed
the author might not even have close vote privileges (like shown here), so it wouldn't make much sense to show them as a close voter.