A bounty offered on a question cannot be awarded to the person who offered the bounty. See the help page.
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 ...
Bounties cannot be refunded. It looks like the answer was given it because it met the criteria for automatic rewarding:
They were posted after the bounty was started, and
They have a score of at least 2 (at the time the automatic awarding takes place), and
They were not written by the bounty starter.
So half the amount was given to the person who got it ...