How is the Reversal badge awarded to this trigo question?

The Help Center shows the requirement.

Provide an answer of +20 score to a question of -5 score. This badge can be awarded multiple times.

In the timeline of the most recent question on the list, no downvote on the question can be observed. How can this question satisfy the requirement of a -5 score?

• We will see whether somebody can find more about this, but this has quite likely something to do with merging. The answer was originally posted to this question which was merged with the one you're linking to (revisions/timeline). – Martin Sleziak Apr 3 '18 at 10:23
• @Martin: If I were a gambling man, I'd say that you're spot on. – Asaf Karagila Apr 3 '18 at 10:42
• Maybe it got few up votes after the badge was awarded. – SmarthBansal Apr 10 '18 at 11:07
• @SmarthBansal That's possible, but I believe merging is more probable. – GNUSupporter 8964民主女神 地下教會 Apr 10 '18 at 11:15

The reason for this behavior seems to be that the answer was originally posted to another question which was then merged with this question. The older question is now deleted but before deleting it got to the score $-12$. So if we take this question into account, the answer satisfies the criteria for the badge.