What they seem to be driving at (from what I can make out) is that he had severely impaired ability to flee.
The thing is, to my mind, he could either have fled towards the bedroom door and lock it behind him, or he could pick up the gun and fled towards the bathroom.
Given that they're talking about how precariously balanced he is on his stumps, particularly if he is carrying something (such as a gun, restricting how many hands he had free to right himself), then he was putting himself in a position of considerable danger if he thought that there was an intruder in the bathroom.
There really was nothing he could do about an intruder in the bathroom other than shooting them dead, which sounds premeditated to me.