Is there anything left out? Past indiscretions, problems with finances, the law etc on your part? Maybe he is planning on proposing, and wants to be sure there are no skeletons in the closet? (Still odd if you are in a trusting relationship)
Also, could the background check have been for someone else? I would assume that the name of the person that he checked was not on the credit card receipt, so are you sure it was for you?