Completely different meanings. They are related. They are not the same. I ask again. How are they the same?
Philisophical materalism
The theory that matter and energy are the only objects existing within the universe, and that mental and spiritual phenomena are explainable as functions of the nervous system of people
Natualism
Only natural things operate the world rather than spiritual
Metaphysical philosophy
A division of philosophy that is concerned with the fundamental nature of reality.
That would mean metaphysic naturalism is looking at the nature of reality without spiritual causes? If so, are they saying this view is a metalistic view?
Id say naturalism is based on materalist view. They are not the same they just have the same approach of defining characteristics of reality (metaphysics).
The answer to your OP
You Dont need faith to believe materalism. Its right there in front of you.
You may need faith in naturalism. How can one proove that there is no spiritual part of the world?