I am studying the difference between Passant and Fußgänger.

I have two hypothesis:

hypothesis 1: Fußgänger is a person who is walking on foot. Both Passant and Fußgänger can be used to refer to a person walking on a sidewalk.

hypothesis 2: Fußgänger is a person who is walking on foot. Passant can be used to refer to a person walking on a sidewalk.

What is the difference between them?

Thank you.