I am not so sure I agree with the others and when you book as a direct flight they would be correct. If I understand you correctly, you flew the earlier AUS-DFW flight and kept your origional DFW-SFO flight: AUS-SFO had the same flight number.
This is what happens in the carriers computer. You had 2 segments AUS-DFW-SFO and the computer had 2 segments. When you checkin, the computer matches a flight with a segment. When you were put on the earlier AUS flight, the computer matched this with your origional AUS flight. It then matched DFW with DFW. In other words, you still had 2 segments (and matches) in the computer and should get credit for both segments. I would not call AA until your flight posts and you see what you get. I think you will get credit for 2.