Mike, you’re thinking the same way I am. Which begs the question; were the rotors also changed or just the pads?
Changing the pads only would be simple with the P-brake on. It would be impossibel to change the rotors with the P-brake on unless the P-brake wasn’t working properly. The drums would hold the disc solid.
Allow me to suggest an alternative scenerio. It’s common when completing a vehicle to leave it in the lot awaiting the customer with the parking brake engaged. Perhaps the shop did the brakes, left it in the lot with the P-brake on, the customer drove it away and after going some miles discovered that the P-brake was engaged, then assumed the brakes had been changed that way…and is now wondering about damage.
If I made that mistake I’d definitely want to check the P-brake pads, as well as the discs for signs of overheating (purply-black diacoloration). Some might argue that it isn’t necessary because the brakes should only be used for parking, but I like to keep the system in good shape just incase I ever need it as a backup. The owner’s manual calls it a “parking brake”, but if I ever put my foot down and the pedal goes to the floor it’s going to become an “EMERGENCY brake”.