A man in a blue shirt, blue jeans, and a red apron standing at a grill.
A man in blue jeans cooks hot dogs on the grill.
We do not know he is cooking hot dogs because the food item is never described in sentence 1.
Not everyone cooks hot dogs every time they use the grill.
Standing at a grill does not necessarily mean a person cooks. There are a number of other items that could be on a grill besides hot dogs.