I have an Amana French Door frige with freezer drawer on bottom (Model: afd2535deb). Today I noticed about 1/2 ice on the floor of the freezer cabin. This was interfering with opening the freezer door. I cleaned out everything and removed the ice (easily) and uninstalled the ice maker. The freezer is now running and cold.

Any ideas on why/how the ice got there?

You could have a sticking water valve or a stopped up drain under freezer coils. Each time it goes into defrost water drains into pan under unit. If you remove cover to freezer coils you can see if it's stopped up. If that's not it then it's likely the ice maker's water valve or even micro-switch controlling that valve.