it very likely is the drum brake being seized, both the front and the back brakes were bad after my van sat for a long time

take the wheel off and try to knock the drum off to inspect the brakes

 

I would suggest removing the locked up wheel on the rear and back out the emergency brake adjuster a couple of good smacks on the drum should set you free, don't forget to tighten up your adjuster again.

 

I had that happen to my 2000 when I had just finished rebuilding the strut towers and went to move it, back in 2009. The parking brake had rusted up. After finally getting the drum off, I found it was where the lever pulled by the parking brake cable attaches to the bottom of the brake shoe, had rusted and seized. The cable was releasing, but the lever wouldn't allow the brake shoe to retract. I got everything apart, cleaned off the rust with a wire brush, and lubed any contact or moving parts with antiseize. Reassembled, worked and released the parking brake to be sure it would release, and refitted the drum and adjusted the shoe clearance/drum drag with the adjuster on the backing plate. It has stayed moveable ever since.