I suspect the bounty was offered by a user (perhaps the OP) whose account since then was deleted. Thus, the ownership of the bounty went to the Community User. — Joel Reyes Noche 2 hours ago

Joel is correct. More information here: meta.stackexchange.com/questions/196716/… — Todd Trimble ♦ 1 hour ago

Thanks, @JoelReyesNoche and ToddTrimble. No need to keep this question open now. — Steven Landsburg 1 hour ago

I will add that if you look at the questions revision history or at the timeline you can see there: "Notice added Authoritative reference needed by user140765." (Although I am not sure whether this message is still displayed there after the bounty ends.) — Martin Sleziak 2 mins ago

@MartinSleziak: I don't understand what that means. — Steven Landsburg 10 mins ago

@StevenLandsburg I was merely pointing out the fact that the username was shown there. When starting a bounty, you can choose one of several bounty remarks - as you can try for yourself if you try to offer bounty, but do not submit it or you can look at the screenshot shown in this answer: How should bounties be categorized?. "Authoritative reference needed" is one of the possible choice for bounty reason. — Martin Sleziak 24 secs ago

@ToddTrimble Perhaps this is closed to the question at hand: When can the community user offer a bounty? (The one you linked is about bounty awarded by the Community user, this one is about bounty offered by the Community user.) — Martin Sleziak 19 secs ago