A woman carrying a large package on her head walks in front of a building plastered with Portuguese posters advertising a concert.
A Norwegian man carries groceries home.
There has to either be a man or a woman that is the subject. A person cannot be carrying a large package on one's head and carrying groceries at the same time.
The person is either a woman or a man; they cannot be both at the same time.
The first sentence says a woman. A woman cannot also be a man.