Not even written in C? Because language interop is a thing, unless one is religously following the mantra of being a X-lang developer instead of embracing polyglot skills.
Just like I used to call Windows DLLs or COM libraries from TPW and Delphi.
Which incidently is how Google pushes everyone to write native code on Android, as little as possible, just tiny native libraries. Even the NativeActivity is just a regular Java Activity implementation with predefined native methods declarations that the shared object is expected to fill in, to be properly called from the framework.