He made a big mistake during the renovation!
This craftsman assembled the frame too early, and the shower stall simply wouldn't fit through the door. To fix the mistake, he carefully cut out two studs, only cutting through the nails, then reinstalled them and reinforced the fasteners. It was quick, clean, and didn't require any dismantling.
Here's an even more compelling description, in YouTube style:
He made a stupid mistake—he assembled the frame too early, and the shower stall simply wouldn't fit through the door. To avoid dismantling the entire wall, he carefully cut two studs at the nails, removed them, and reinstalled them, reinforcing the fasteners. Quick, neat, and very clever.