<p>There's a <a href="https://meta.stackexchange.com/questions/91922/how-was-this-answer-posted-after-this-question-was-closed">grace period</a> after closure where an answer can still be accepted (however the <code>Post Your Answer</code> button becomes disabled, so you have to be clever enough to find a way around that).</p>

<p>In this case the posting of the answer came so close in time after closure that the button was probably still working at that moment. </p>
