First off, sorry for the non-honda post, but the car in question is my fiancee's junkbox Kia Spectra.

I had yesterday off from work because of the blizzard, but she had to work. So i took her to work in her car, then drove it down to my parents house to put the new pads on since she needed them to get an inspection sticker.
Every thing went smoothly, and i got her sticker, and later went to pick her up for work.
Now, it was still blizzard conditions when i picked her up (we got over a foot of snow ), and as soon as we left her work i noticed something funny. The back end of the car was super loose around corner. Normally the car will plow on a snowy corner, but the rear was stepping out super bad. Also, intermittently, it would seem to accelerate very slowly.
Since i was on the highway, and could barley see, i didnt worry about it. There was no way i could pull over.

This morning, i go to move her car, and her left rear wheel is not turning while going forward, but while backing up. You can also see where the tire had melted from being dragged during the ride home.

My question is, is there anything i could have done to cause the a rear caliper seize? The new pads were very thick, so i had to push the pistons in really far. Could this have done it (even with the brake fluid cap off)?
Any other ideas?
Our street is all ice, and i can't really jack the car up right now.
Thanks.
The Captain.