Sorry, forgot to update this.
It was confirmed by me and a mechanic friend of mine that the shop did not cause this damage. The control arms were bent not from the bottom up, but from the rear back. It seems that at some point in my car's life, someone tried to pull it (perhaps out of a ditch?) by latching on to the control arms.
One crucial detail I forgot all about was the fact that I had just swapped my tires (front to rear, rear to front) and the tires now on the rear had much less tread than before. So when I was driving it on somewhat slick roads, with little tread, and bent control arms, now I began to really feel what was going on back there.
The good news is, they fixed it, showed me the damaged control arms (also in pictures before they pulled the old arms off), and split part of the cost with me. They are still a good shop and I recommend them to anyone... :nod: