Correct on your assumptions. The build system is CMake and until I manually installed ncurses from source, it was not finding ncurses. Basically the CMake find_package() module for ncurses scours a bunch of common locations looking for the lib and include and then tests for certain symbols to determine if it has wide support. What it finds (or the lack thereof) determines how / which include paths are supplied to the compiler.
On a semi-related note... as I port to other systems (FreeBSD, OSX, and even other Linux distros), it's bizarre that there doesn't seem to be any consistency as to where the OS provider deploys ncurses. It seems to be a point of frustration for the CMake guys as well.