Stopping the torrent was your biggest mistake. See, your torrent client only updates with the tracker once every 30 minutes. If you stop the torrent before it updates with the tracker, then it does not update with the tracker, and the uploaded data is never credited to you because it isn't reported to the tracker. THAT is likely why you didn't see much upload traffic. You stopped the torrent before it was able to update with the tracker.
Wouldn't the client report the "stop" behavior to the tracker so it can remove the user from the seeding list? How could it not report the upload traffic also?
Just my guess. I'm not an expert of it.