As the title suggests, the NDK automatic lookup feature seems to prefer a tarball over the extracted NDK path, so I have to specify --ndk-dir manually.

[INFO]: Found possible NDK dirs in buildozer dir: android-ndk-r9c-linux-x86_64.tar.bz2, android-ndk-r9c
[INFO]: Will attempt to use NDK at /home/cheaterman/.buildozer/android/platform/android-ndk-r9c-linux-x86_64.tar.bz2

Thanks in advance ^__^