Just watched that video and no way that boa is 12 inches in diameter or 10 ft long lol.
I tried to gauge a size on it but really no reference to use other than maybe the fence. If each square mesh in the fence was say 4 inches, being generous and say it is 20 mesh squares long(i think more like 15 but i'm giving the benefit of the doubt), that would make that snake 6.7 ft.
As for being 12 inches in diameter, there is no way. If you look at the head of that snake, it can easily fit in a mesh square with room to spare. So that would mean the head is probably 3 inches or so. That would mean there is no way the body is 12 inches in diameter since that would make for a very disproportioned snake with a head 3" wide and a body 4 times that wide. Using the mesh square to guess the head and then using the head to guess the body, i would guess the body is about 6 inches in diameter.
He/she is actually a pretty healthy looking snake as you can see its squared body shape and it being taller than wide. You can also see the muscle line down the side in some of the video which means it doesnt have a ton of fat on its flanks. It does have a couple lines running down each side of the spine on top but they look good, not like a Grand Canyon effect which is another place boas store fat.
But anyways, there is no way that snake is 10 ft and 12 inches in diameter lol. You see all kinds of people claiming their boas are 8 or 9 ft and then if you actually hit them with a measuring tape, they shrink in size quicker than 'manhood' in a cold swimming pool lol.