2000 GMC Truck Brake repair gone wrong?

I had taken my truck in for repair as the the brakes were making noise and slow to stop. When I picked up the truck I was advised that the brakes were not in need of repair but instead were cleaned and adjusted. The receipt read: "Remove dual rear wheels, inspect shoes, drums, wheel cylinders and hardware, replace and torque to specification".
A few weeks later the rear brakes seized and caught on fire on the highway necessitating a tow for the truck and a horse trailer. The brakes had to be drilled off of the truck and the truck required new rear brake shoes, wheel cylinders and adjustment. I was told by the mechanic that the linings were paper thin.
My question is- what did this first shop do wrong or not do at all?