In an attempts to solve my brown paint mystery, I sent my wallpaper stripping pictures to a friend who specializes in historic interiors. Her theory is that I may have had a very heavily textured or flocked wallpaper on the top half of the wall at somepoint, and lincrusta at the bottom. An online friend had voiced this suspicion based on her own home restoration efforts, and it looks like she was correct!
Having heavily textured anything would have necessitated taking everything off before anyone put up "new" paper. The brown bottom could be paint mixed with an adhesive of some sort.
Even though it's not original, I'm still going to keep the little square of early paper. I will frame it as it sits on the wall. :)