It looks like they've done it through automod actions, so if you type a comment like "!lock" automod will lock the thread for you. Other things like downvoting a comment to below -8 results in the user in question receiving a temporary ban. Apparently they are hard at work on new commands to let all users run roughshod over the sub.

Your wish is our command: Here are your new moderator permissions.

• To lock the comments on any post, simply comment !lock as a top-level comment on any post.

• To unlock the comments on any post, vote the AutoModerator stickied comment on each post high enough, and comments will be unlocked.

• To lock any comment on any post, reply to it with "!lock".

• To temporarily ban any user, simply get their comment or post to a -8 score.

• To remove any submission, reply to a submission with a top level comment of !remove. Must have sufficient subreddit-level karma.