It was not clear when your friend made left turn.

Based on your message, I believe when your friend started to make left turn, the other car was coming toward the intersection, no matter the other car was on the right lane or left lane. Therefore, I think firstly it was your freind's fault: not yeild to the coming traffic when he/she made left turn. However, the other party should take part of responsibility for the accident. The other party did not check carefully (looking back) when he/she changed lane: reckless driving.