About an hour ago I posted an answer to this question. When I viewed the question there were no answers. About thirty minutes later, I viewed the question again and saw that this time there was an answer that had been accepted. And that answer had been posted 4 hours ago. And there was a comment by the OP thanking him for his answer, 30 minutes before I had posted mine. There wasn't a whole lot of time either between when I viewed the post and when I posted an answer, no more than 10 or 15 minutes. I deleted my answer because it didn't really add to the accepted answer.
I checked the answer, but I didn't check the question!
You're right, there was no answer on the question when you answered it. That's because you were answering a different question. The merge happened shortly after you posted your answer.
I'm concluding that your answer was on the merge-from question, as the other answer doesn't have merge history in it and you have a revision on the other question. My guess is, when you went to re-look at the question, you did it by visiting your answer. That now directs to the merge-to question, so it looks very awkward indeed.