I'm not sure if this is a house rules thing or not.
So I am playing a battle royal, three players, new venue for me.

So on player 1 turn he attacks player 2 and deals damage to player 2 piece. Then on player 2 turn he attacks player 3, crit misses, and KOs his own piece.

So my thinking you crit miss ko on attacking player 3 (me) I get the points. Their logic is the points got to the person who last dealt damage to that ko'ed piece. Player 1 gets points, he wins night.

Who gets the points? player 1 or player 3

Player 1 - it's the player who last dealt damage to the piece. It's the same reason your opponent gets points if you push yourself to KO (Since you can push to move and get KO'd, giving your opponent the VP). It has nothing to do with who they were attacking.

Rulebook p. 17

When playing with more than 2 players, victory points from defeated characters or removed objects go to the player who was active when the character was defeated. If a character was defeated on its owner’s turn, the opponent that has most recently damaged the character earns the points. If no opponents damaged the character, the points are divided evenly.

Yeah - that's what I was trying to say!