It also wasn't reasonable because he could have escaped, but chose to confront the danger instead.
It also wasn't reasonable because as an experienced, licensed gun owner, he knew shooting an an unseen/unidentified target is illegal.
It also wasn't reasonable because even without ear witnesses, the pathologist confirmed that Reeva would have screamed after being hit in the hip with the first shot indicating to OP it was mistaken identity, or at the very least there was no more imminent threat since he incapacitated the intruder, but he changed his aim and fired again...and again...and again.
It also wasn't reasonable because he was composed and thinking clearly enough to approach the bathroom cautiously, looking around corners, holding his gun in a manner that an intruder couldn't grab it, didn't fire a warning shot because of the ricochet, but then became a fumbling fool who pulled the trigger without thinking because he was startled. He was awfully cool and collected right up until the moment he suddenly "didn't have time to think," and the shots just fired out of his gun like an involuntary knee-jerk reaction.
Totally and completely unreasonable.