My walkin closet is 12ft X 7ft...and my SKS would be easy to handle in there. Depends on how deep the closet is.
My hunch, is he was crouched down, with muzzle pointed in an upwards position...When they entered, he just started squeezing off rounds as fast as possible.
My bet would be, costly mistakes were made by the entry team, after two of their own were killed. They wanted this guy bad, and took too many chances.