actually, a gun could 'just go off' if you had a case commonly referred to as "the hand of god." or left a round sitting on black concrete, with a magnifying glass sitting on top of it, in AZ in the middle of July, and it managed to get hot enough to ignite.
Otherwise, no, a round does not just fire of its own free will.
As to the OP, unless his brother comes in and testifies that he tried to kill him or something, I cant see him being legally barred from owning firearms. Yes, he needs to learn how to properly handle them, not to mention how he managed to discharge it in the middle of cleaning (sounds like it was in the middle of cleaning, so i would assume the rifle was partially disassembled). I see it as: he needs to learn proper gun handling, but thats about it.