OK, my first thought was did you use Epsom Salts ? That might help you in the future being as how it seems to force things out of us at a faster rate. If you didn't use the Epsom Salts , be grateful it didn't get stuck because a stone that size could probably have gotten you a trip to the emergency room!
As for the size, yes that is possible and has happened to others. Blueduck from this forum passed a stone that was so big it barely fit into a baby food jar! She was kind enough to send the photo to my e-mail and boy was it a whopper!