Although the mother was getting beaten, I can't sit here, and say she didn't provoke him. As far as we know, she started the confrontation.
I want everybody to put themselves in the decreased shoes for a moment. You're at the window, and you already paid for your food. The altercation is now over as far as you're concerned. But this women, instead of picking up her food, decides to stop in the mans face, and continue the argument, speaking in a loud voice, and refuses to get her food and leave, like the man requested. Instead, she stands there, and watches him get louder and louder, until it becomes a physical threat. That's not the way to go, nor was texting her son, knowing something was about to go down. At this point, watching her texting somebody in his face for backup, could have been seen as a threat as well.
I bet if that was a woman, and the mother did the same thing, getting in her face speaking loudly, while ignoring her, she would have got popped in that situation too, especially if that woman was bigger. With all said, that man's actions were still wrong. But next time, let She neh-neh go toe-to-toe with a complete stranger, while you say your peace and keep it moving, or just keep it moving.