I'd just leave it. You have done all you can and by doing anything further you could cause bad blood between you. Some people just don't want to be helped.

By left curb you mean he went to the wrong side? (being from the UK the left curb sounds logical to me!) If so then that is pretty stupid as the car was probably trying to overtake and he crossed infront of them.

Many people don't want to run a mirror for fear of looking dorky - personally I love my mirrors.