It's a superset of Python. What you call "Python" is actually CPython, a C implementation of the Python language. Many other Python implementations exist, though they typically don't support all packages well (for example lack of support of native Python extensions like what Numpy relies on). It looks like Mojo has its own runtime (so not CPython) but also packages CPython for compatibility?

Wrong, Mojo is not a runtime for Python.

This is like C++ to C - so python++, ++ is for features and native compilation