Closing a thread about a topic that already has a thread going on is fine, its good practice to keep a forum clean and streamlined, the way TDA did it was, fittingly, childish.
He's a child and he is rude and impertinent because of that. He clearly favours some posters over others and not in a way that helps to build community, had eldargal started the thread about Primarch prowess, no doubt he'd be agreeing with everything she said in the thread right now.
He's not a good moderator at all. He'll probably ban me for this.