I am also deeply skeptical of the net-negative claim, mostly because of the outsized role plywood appears to play in the building productions demonstrated. There are several energy-intensive steps required to manufacture plywood that are not present with standard lumber production. Additionally, transport overhead is higher due to the comparative rarity of the specialized mills used to create plywood. Unfortunately I haven't been able to find any kind of real numbers comparing the carbon footprint of lumber vs plywood to demonstrate exactly how much more carbon it takes to manufacture plywood vs lumber.