They do not coil not because they are fat or obese, but because that is how they seemingly prefer to lay. For example, reticulated pythons are often seen resting in coils, and even ball pythons will rest in a loose coil. Contrary to this, bloods tend to lay loosely and sometimes quite stretched out. I've seen this in juveniles to adults; they are not tight coilers. Even the snake in your video is not tightly coiled when you take him out of the mulch. Has nothing to do with weight.