This answer recieved a bounty of 50 from Community.
Why? What's the algorithm/reasoning behind this?
Most logical answer is that the bounty was automatically awarded on the 10th (or 11th) and the accepted answer was posted after the bounty was awarded.
How is a bounty awarded?
The bounty period lasts 7 days. Bounties must have a minimum duration of at least 1 day. After the bounty ends, there is a grace period of 24 hours to manually award the bounty. Simply click the bounty award icon next to each answer to permanently award your bounty to the answerer. (You cannot award a bounty to your own answer.)
If you do not award your bounty within 7 days (plus the grace period), the highest voted answer created after the bounty started with at least 2 upvotes will be awarded half the bounty amount. If there's no answer meeting that criteria, the bounty is not awarded to anyone.
So it might just (barely) fit the time window for an automatic reward and it does have 2 upvotes.
Come to think of it: he now accepted answer probably did not have 2 upvotes when it was awarded.