It does indeed appear that your bounty was refunded as part of the question being deleted.
The answer is at When a question that had bounties is deleted, are they automatically refunded? which shows bounties being refunded. This is a feature, not necessarily a bug.
If you were to place a bounty that was successful and/or got an upvoted answer you would not be able to get the bounty refunded after a question is deleted.
Bear in mind that any upvoted answers will block a question from being deleted and as a result will block this kind of abuse.
It is not an "infinite bounties" hack, more it is a refund of wasted points.
In this particular case you lost the points from the two upvotes your question had, and got your points lost as a bounty back.
There is also a question on Meta Stackechange How does the bounty system work?
What happens if a question where I awarded a bounty later gets deleted or migrated?
If a question on which you have started or awarded a bounty on later gets deleted, then in most cases, your reputation is refunded. It can take a few minutes for this to happen. If the question is later undeleted or migration is rejected, the reputation is deducted again.
There is one exception to the above rule, however: if the bounty was awarded to an answer, and the author gets to retain their reputation upon deletion (i.e. their answer earned a score of at least 3 and was visible for at least 60 days), the reputation is not refunded to the bounty starter.