Hold on here. I'm calling BS on this one.

If you had NO brake pad on the inside then the caliper piston was pushing up against the rotor, with no pad being there. The piston would have fallen out and you would have lost brakes on the one side of the car.
Secondly there is no possible way for the pad to fall out of there.
I dont belive for one second what you claim.

Secondly dont you ever lube your caliper slide pins, I do mine once every year on my cars. Do a full brake inspection, suspension, everything man.
Maybe thats why they were stuck in there. By the way if it was stripped that was whoever installed them last, they dont get sripped removing them, they get sripped INSTALLING them, same goes for lug nuts, thats why the first few turns you use your hands, so you dont strip them.