Why? More like how. How did the painter obtain a sample?

My guess is that he didn't. He made a requisite and obligatory trip to the house and he's going to go buy gallons of his preferred brand's "Navajo White". Which he would have done whether he came to get a "sample" or not.

He's probably just going to find something close to the color that is on there. Also, there is always a chance to find a can of paint that was used in the basement or a closet.

Point...Is this guy going to paint my walls gray....Of just do a cheap job by matching the dirty walls

Why do you care? At least it is getting painted.