Sorry to hear about your misfortune.
Although I haven't heard of any other broken springs in the automotive field, in industry they are fairly common. As some info:
Generally it is not a single "big bump" that will break a spring, so don't let the dealer try and say your driving was at fault. 99.9% of the spring failures I have examined were due to fatigue. Just the every-day spring motion, not any type of overload.
What happens is that the spring is made from steel "wire" (they call it wire even though it may be 1/2" in diameter) This wire is drawn through a die to shape it and then formed around a mandrel to give it the coil shape. Then it gets some heat treatment processes to make it springy.
In this forming and shaping process, the metal is still relatively soft and if the dies aren't alligned perfectly it can leave a small scratch in the metal, or if something happens to hit the spring and leave a dimple, or even some imperfection in the metal itself. Either way, this small imperfection is like scoring a sheet of glass...it will concentrate the day-to-day stress applied to the metal and make it fracture, even though the stress is well below what the metal could normally take in a "pristine" condition.
This is probably a couple paragraphs more than you wanted to know, but bottom line...unfortunate bad luck, should be replaced under warranty, no fault of you or your driving.
Good Luck