The return type of np.count_nonzero() is currently somewhat inconsistent:

• A builtin integer is returned if axis is None and not keepdims.
• An np.intp (or an array) is returned otherwise.

The former case is handled by the an identically named function in the np.core._multiarray_umath
module (which apparently always returns an int) while the latter is effectively a wrapper around
np.ndarray.sum() with its dtype explicitly set to np.intp:

Reproducing code example:

MacOS 10.15.6; Python 3.8.5; NumPy 1.20.0.dev0+eb2c751

In [1]: import numpy as np

In [2]: ar = np.arange(10)

In [3]: np.count_nonzero(ar).__class__
Out[3]: int

In [4]: np.count_nonzero(ar, axis=0).__class__
Out[4]: numpy.int64  # i.e. np.intp