super hans
Assistant Pro
I wouldn't be bothered. No-one got hurt.
I have hit balls past groups in front on the odd occasion by accident. It happens. A quick apology and get on with enjoying the game.
If someone did it a few times then I would wait and have a chat with them. My reaction to them would depend on their attitude.
All the posts on this where people are getting really vexed and saying that you would whack their ball in a lake are ridiculous.
I wouldn't want to play within a hundred miles with someone who knows nothing about golf etiquette - where do you play