Watch to figure out what's going on.
Unsure of just how to react, you watch to see what the problem is. They're both shouting, but a mall security guard is already approaching. From here, it's only a couple minutes before the young woman is being escorted out. You saw the whole thing, but still aren't sure what happened. It's none of your business anyway, you suppose.
Move on with your life and keep shopping. Follow the young woman outside. Go talk to the man about what happened.