You are very lucky that it happened at a low speed! Do you have a vehicle inspection system in your state? That kind of wear might have taken years to develop in that car. I can't remember ever seeing a loose lower ball joint in a Galant.
The only way to detect that problem is to raise the wheel from the wishbone so that the spring pressure isn't affecting the ball joint. Of course your mechanic wouldn't know that...
Well that's what I'm aiming for 
Your repair shop didn't break anything. The joint was so worn that the ball popped out. They should have detected it though, if they carried out a service inspection on your car, not just an oil change or something(even then unlikely).
