Improper brake pad installation

What is your question?

I recently changed the front brake pads in a family members 2011 Nissan Sentra base model. I haven't changed the pads in a car in quite some time, but I thought I would be able to manage it. I thought I did a decent enough job and when I took the car out to test the brakes, they worked great. However, after a bit of driving the noise came back that was present before the brake change. Its at this point I decided a mechanic should take a look. Another family member took the car to the shop and when they got back I was a little surprised. The shop had said that the brake pads where installed improperly and that they were no longer useable. They ended up replacing the brand new pads with different, more expensive ones as well as changing the rotor and they send the pads I had put in back with my family member and told them to hold on to them and use them on the future, which doesn't make sense because they said they can't be used? Can you install brake pads so improperly?