How could he have known that firing 4 shots into a confined space could've killed someone?
I'm puzzled too but from what I heard I THINK it is because it is determined by OP's INTENTION at this stage, and the judge clearly believed OP's statements to police etc on that fateful morning that he didn't intend to kill anyone - that he lacked intend.
Culpable homicide however is a test of recklessness and would a reasonable person think their actions would kill - OP has to FAIL on those grounds surely.