I don't think you read the bounty rules. The email links to the bounty rules; click that link.

https://serverfault.com/faq#bounty

Auto-award can only occur when

- answer is provided *after* the bounty begin
- answer gets at least 2 votes

The one answer isn't eligible because it was provided long before the bounty started.

(you can mouse over the "in 22 hours" part of the bounty message to see the start and end dates of the bounty, but since bounties only last 7 days, and that answer is from *more than 6 months ago* it's kind of obvious in this case...)