I think his lack of reverse lights was to his detriement. The OP coudln't have know he was intending (if he was) to back into that space, and since another car was leaving, I would have probably made the same assumption, that he was waiting for that spot, NOT wanting to back into the very small spote he had just driven past.
I had a parking situation myself the other day, but I'm pretty sure I was in the right. I came down a parking aisle, and saw a car pulling out. I put my blinker on, and AS I was pulling into the spot, another car came around the other end into the aisle. She then gave me a dirty look, as if I had stolen her space, but the whoel time the car whose space I took was pulling out, she was nowhere to be seen, so I'm guessing she was in the next aisle, saw the car pulling out in mine, and decided to come around and park there, perhaps not seeing I was already waiting, and signaling for that spot. I just parked and got out, and went on my merry way.