The federal government, through the GSA, sells literally hundreds of tons of range brass. I believe that most of this is swept up from solid floor ranges, not scrounged from the dirt by hand.
Would the guy be rummaging around and collecting it for salvage value? Unless he's living on ramen, I can't say. If he is collecting it for himself and lying, he is probably selling it to a dealer who re-sells it.
Our scrap yard had about a dozen barrels of used brass, it was kept separate from any other metal. That's not going to be melted.
My range has a written policy, collect and remove all brass and debris. When I'm there and alone, I gather whatever is on the ground until I get tired. I get back what I shot and some more. I also gather the aluminum and steel, dump the aluminum in a bucket, toss the steel into the trash. There's nothing to be gained gathering aluminum brass, 45 cents a pound? I don't like waste, or I'd leave it there forever.
Apparently, I'm not the only one who does this, because sometimes the range is clean of all brass but buried elbow deep in steel and aluminum.