Rear wheel locked up after rolling 10 feet and smoking front wheel!

Nothing large fell out but there was some smaller debris. You can see most of it in the last photo, I took the pics before I sprayed it down with brake cleaner. I was looking for that chunk of shoe but didn't see it. I only drove around the block and when I returned there was no smoke, no "hot smell" and I felt the caliper and front end components and nothing felt hot. Discs were warm, but both were about the same temp. I was afraid to take it more than a mile!