Over the past week or so, I've seen multiple questions (such as this one) that have popped up on the activity page saying that they've been reopened. At first, I just passed it off as users accidentally closing their questions and then reopening them, but, after seeing more, it didn't seem likely to me that multiple different users made the same mistake within such a small period of time. What's happening?
This should be fixed now. It was an error that occurred when selecting best answer for a question.