JanB

I play golf .. and in my spare time 😉 - I run a company that has developed a gamification golf app called GolfQuis (Rules of Golf).

If just a small part of your ball was below the surface of the green - the ball is considered holed. (rule 13.2c) So no penalty - and your friend was just unlycky by hitting your ball and has to play his ball from the new position.