Even though Matt Kucher is keeping pressure against his forearm, it is not decreasing the motion of the golf swing, meaning both arms have to swing to make a stroke
If you anchor a long putter against the chest or chin, or belly putter against the gut, you then create a motion that is not a stroke since the one end is not free to move.
Kutcher holds a putter like a normal grip, he just make sure the his grip touches his forearm, its a feel mechanism for him. There is still a chance for him to loose that contact if the stroke breaks down. Anchoring in the other fashion makes this impossible.