He intended to kill whoever was behind the door, or at least he didn’t care if he did or not when he pulled the trigger.
TBH a gun is for killing people with, it’s possible to shoot to wound but even for trained marksmen that’s not how it’s done. If, arguendo, you accept that he did think there was an intruder in there, he’s a disabled man with a gun, shooting to kill (or at least shooting in a way that was likely to kill) becomes a lot more reasonable.
Unless you think you could shoot someone to disable them, through a door?
I don’t think I’d have shot someone in that situation. But then I’m not a paranoid disabled celebrity dude in south africa.