Picture will make it more clear:
I guess it's due to the user having 1 reputation and can't get below that but still - couldn't figure what exactly triggered this line of information.
Also thought maybe it's the automatic -1 for questions closed as NARQ but it was closed back in March 14 while the super downvote took place at March 30th.
More details: when viewed by post, it shows "2 events" for that post:
-3 08:31 2 events guideline for web devlopment -1 08:31 downvote -2 08:23 downvote
So this looks like a bug with the group by time, showing two events that didn't happen in the same time together.