He didn't break the law because he never filled out the form for the AR15. He was pictured filling out a form, but it was for the .45 pistol he was buying for himself. The AR15 purchase was on hold because it was a used firearm and had to clear a 20-day waiting period to see if it was stolen. He was going to fill out the form then and take possession.
To the store's everlasting credit, they cancelled the sale and told him to never return to the store when he tried to make a circus of it, while smearing them at the same time. "His business is no longer welcome there."
Thanks for the assist.