I used to do that to drag racing slicks to make dirt track tires. He is a strong son of a gun and he has done that a few times before!
Funny story, when I was a young man I had got my hands on some ten ply lowboy tires that were the right size to fit the front of my 7/8 ton Chevy truck. Tires for the truck were expensive so I ran them almost to the quick! When it came time to get an inspection sticker the tires were slick and I was low on cash. I heated up my trusty grooving iron and applied another layer of tread just like he is doing, then I took it to a friend's to get the brake tag. He looked at my front tires, "You aren't an outlaw but you sure run close to the wind!"