A man in a blue shirt, blue jeans, and a red apron standing at a grill.
A man in a blue shirt stands by a grill.
Standing at a grill is the same as stands by a grill.
The man is in a blue shirt by the grill in both cases.  Details are simply left out in the second sentence.
A man in a blue shirt, blue jeans, and a red apron because he is standing by the grill.