Purely general experiences of mine: aside from occasional caliper sliding pins (NAPA carries them, probably others), I have had the caliper bore develop a glaze of residiue behind the range of stroke currently in use (meaning as the pads wear there is only a modest area that the piston is moving over).
It is also not unheard of to happen coincidentally with a tire change -- why? The calipers get bumped/moved during the install/rotation (they are just sitting there and not being worked, so they can/should be free to move). May not apply to your issue, just something to keep in mind.
Most brake problems are due to lack of fluid flushing. If you brake fluid is other than clear, it is on its way out (normal -- it absorbs water and you just can't seal it from eventual migration). Most manuals will tell you to replace it every two or three years (or have a mileage limit).
It is also not unheard of to happen coincidentally with a tire change -- why? The calipers get bumped/moved during the install/rotation (they are just sitting there and not being worked, so they can/should be free to move). May not apply to your issue, just something to keep in mind.
Most brake problems are due to lack of fluid flushing. If you brake fluid is other than clear, it is on its way out (normal -- it absorbs water and you just can't seal it from eventual migration). Most manuals will tell you to replace it every two or three years (or have a mileage limit).