I was trying to put a vote to close this question as a duplicate, and it was closed immediately with my single vote. I thought only mods can do that.... What gives?
Your expertise in the tag let's you mark dupes directly.
My understanding is you can close dupes with your single vote because of the trust you earned, but your vote is normal putting something on hold.
Users With Gold Tag Badges Can Unilaterally Mark as Duplicate
A user who has the gold tag badge, (which requires at least 1000 score across 200 answers) can mark questions in that tag as duplicates using a single vote, similar to a moderator. The question must have had the tag in its original posting, and the target duplicate must have an answer. These users may also unilaterally reopen questions marked as duplicate in that tag, in cases where the question shouldn’t have been closed, or when there is a more appropriate or complete target question. When such a top user closes a question, a gold badge icon will be displayed after their name in the close reason message.
Here is the Meta post: