It does indeed appear that your bounty was refunded as part of the question being deleted.

The answer is at https://meta.stackexchange.com/questions/145329/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.