I think I agree with you. I think it's just the bile that gets flushed out. Of course I haven't seen any medical proof with scans so I don't know for sure but that's just my gut feeling (excuse the pun). :)
I think when people get these huge Gallstones the size of golf balls it's actually just a lot of those little squishy balls that clumped together in the gut. I don't think you can get a golf ball out of a duct like that. The magnesium might relax the duct but not THAT MUCH that it can give birth to a golf ball?