<p>That question is not closed. It is not possible to add answers to a question that is actually closed. See this <a href="https://stats.stackexchange.com/q/3473/28">question</a> as an example of a closed question.</p>

<p>The question you linked to has an 'accepted answer' which does not prevent other users from adding answers as you yourself did. When a new answer is added to a question or a question is edited that question is bumped to the top of the active questions which enables others to see the new answers and/or question edits.</p>

<p>I am sure several users have seen your answer and would have left comments if they felt that they were confused about some aspect of your answer.</p>
