The bounty simply seems to have disappeared and they did not get awarded the points for their answer.
The user answered their own question after the start of the bounty and it has a score higher than 2, so it meets this criteria taken from the FAQ (https://gaming.stackexchange.com/help/bounty):
If you do not award your bounty within 7 days (plus the grace period), the highest voted answer created after the bounty started with a minimum score of 2 will be awarded half the bounty amount (or the full amount, if the answer is also accepted). If two or more eligible answers have the same score (their scores are tied), the oldest answer is chosen. If there's no answer meeting those criteria, no bounty is awarded to anyone.
If the bounty was started by the question owner, and the question owner accepts an answer posted during the bounty period, and the bounty expires without an explicit award then we assume the bounty owner liked the answer they accepted and award it the full bounty amount at the time of bounty expiration.
Or does the fact the bounty have to go to a different user override this automated mechanism?