Spoiler alert. Don't read this post if you don't want to know how it was done.
The real trick was gluing the magnets to the ends of the rope which become the center of the rope. Notice how he pulls the rope before pushing the block out and as the block moves out a short section of rope inside the handle with magnets on each end drops down the magnets connect and now you have a solid rope but it is about 3 inches longer. Note when he picks up the rope how he hides the center. The plastic red thing is nothing but a distraction for your brain