“He and his caddie didn’t think he’d addressed his ball, but they didn’t know the definition of the rule.”

Rex Hoggard gives us a little more detail on the Joost Luiten DQ:

"He took his stance which means you’ve addressed the ball and then the ball moved which is a penalty,” said PGA Tour rules official Jon Brendle who was involved in a lengthy conversation with Luiten adjacent Muirfield Village’s chipping green after the ruling. “He and his caddie didn’t think he’d addressed his ball, but they didn’t know the definition of the rule.”

Luiten violated Rule 18-2b and failed to add two strokes to his score on the hole. Because he had already signed his scorecard he was disqualified.