I was facing misdemeanor B theft charges, but I completed a pre-trial intervention program and it said that my case was dismissed.

Yes, you were charged, technically, but never convicted. An expunction would be a great way to clear your record, wherein you could later claim that you were not even charged!  This is the main reason a pre-trial diversion program is advantageous. You should be able to join the Navy as an officer, regardless, based on my limited understanding and experience in that specifically, but any recruiter could answer that question.