That's one of their few parts that breaks, and just like anything, you'll run into it every now and then. If you bought the shocks new, they should warrantee it given you can prove you broke it how you did (show pictures), if not, you can still try it but if you don't have a receipt you might be SOL.
Only other thing I can think of why they broke, besides a random defect part, would be that the shock was frozen for a while and therefore couldn't compress, so the shaft, not being able to support the weight of the truck, snapped. Either that, or the truck came down too hard/fast for the shock to compress enough to releive the tension. It takes some doing to get Bil's to compress, so it could've very likely been that it fell too fast for the shock to react.