Here is a picture of a man waiting for the bus to pick him up and he is hiding his face.
The man doesn't want to be seen.
Hiding one's face while outside doesn't necessarily mean the man doesn't want to be seen. He may be shielding his face from sun or wind.
While the general assumption of someone hiding their face is that the man doesn't want to be seen, it could simply be that he was cold or not happy with his appearance.
Just because the man is hiding his face does not mean he doesn't want to be seen.