Steve, I've investigated many of these type failures over the years. One resulted in the total collapse of a barn. The homeowner left for work in the morning as the supplier was stacking shingles along the peak with a conveyor. When she got home that afternoon, there was just a big pile of debris where the barn once stood
In other cases, the tops of the walls are pushed out a few inches, creating instant 'skylights' along the tops of the walls. In metal plate-connected truss roofs, it often causes the metal plates to pop loose and nobody ever knows until years later when a home inspector finds them or a snow load collapses the roof.
So if the bundles of shingles were all stacked up along the peak of your roof, they took a huge gamble at your expense (hopefully, you took photos). The bundles must be spread out individually over the entire slope of the roof to simulate a uniform load. Most roof structures are not designed for a concentrated load along the top. Sometimes roofers get lucky and nothing happens.
The reason they stack them along the peak is simple: it makes it much easier to lay the shingles with nothing in the way.