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.