There is a very big difference between going around a turning driver on a two lane road with plenty of room on the shoulder then having to make an emergency move in a parking lot because the OP didn't plan well. She endangered a great deal of people with her move and the what ifs are endless. Just because she couldn't see something in the way doesn't mean it didn't exist and she would have had no time to react because she was trying to get out of the way herself.
I will absolutely politely confront someone about their driving behavior when it endangers myself and others. I've had enough of my friends killed because of the stupidity of others. He asked her to have some patience and simply said, "Jeeze, you almost clipped me." He didn't yell at her, he didn't use extreme profanity, he simply asked her to have some patience and to pay more attention. Not wrong. If the roles were reversed, I'll bet we'd be congratulating her on having a shiny spine.
The OP didn't even really think she had made a mistake until it was pointed out to her here. Now, she'll probably never make the same mistake again. He made an impact and that's why I speak up. If me speaking up makes the other driver uncomfortable but a more aware and a safer driver, why is that wrong? People get away with bad behavior all the time because no one speaks up.