how can OP sue such an action.
I suspect you already know this, but you can't sue because the moderator of a website did something you don't like. About the most you can do is bring it up on meta like you already have
He at least could wait for other moderators to vote for close up.
Moderators can't vote, they just act. If you mean he could've waited for other users to vote, I suppose so, but moderators are elected because they understand how their respective sites work -- their judgement is generally pretty good
Closing a question on a single thought is true dictatorship and egoistic
It's not a dictatorship; again, they were elected. And I know ChrisF well enough to be confident he doesn't get an ego boost closing questions, he's just trying to keep the quality of the site high. The FAQ explains what questions are off-topic