First things first - please be civil. There's no need to call someone 'blind' for voting to close a question - please give the benefit of the doubt that they did so in good faith.
On to the issue. The question has a single close vote (as you can see in the screenshot you posted), it's not actually closed. I can't see anything in the edit history to suggest it has ever been closed.
To address the new question you're now asking
Why this question marked as duplicate?
Questioning individuals' motivations for voting to close a single question, one time, isn't really a constructive area of discussion. I would say you can boil it down to one of these reasons:
- The voter made a mistake (it happens) or
- The voter genuinely thought that your question would be answered by the proposed duplicate
Either way, your knowing the 'real' motivation (if there is such a thing in this case) doesn't help anybody. It was voted for closure as a duplicate, so (in my opinion anyway) the answer to your question is that it was marked as a duplicate because the person doing the marking thought it was a duplicate.
Unless 4 other people agree with that assertion, you have nothing to worry about.