What happened is that the person who posted the bounty never awarded it.
Per the help center:
Bounties expire after seven days. You will receive several
notifications a few days before this happens.
If you do not award the bounty within 24 hours of the bounty period
ending, half the bounty value will be automatically awarded to the top
voted answer posted after the bounty start, provided it has a score of
at least 2. If no new answer matches this requirement, no reputation
will be awarded at all, and the reputation used on the bounty will be
Note the part that I emphasized. The bounty was started on February first, after you had already posted your answer. The answer that was awarded half of the 100 point bounty was posted on February 2nd.
The person who posted the original bounty had a period of time during which they could award the bounty. They did not (presumably because they're quitting the site), so the auto-award clause kicked in.
Note that the person who posted the bounty has not deleted their account. The offering of the bounty still shows their name in the edit history. It is only the awarding of the bounty that shows Community, and that is because the user didn't actually award it.