Not really the way that guy was going at him it looked like he intended to do something similar, but also an attacker should be prepared to face not only equal force but greater in retaliation.
maybe, we do not know his intentions. Hitting someone when they are down is not self defense. But yeah, the scene is pretty unclear. Maybe he was just trying to get back up, maybe he was attacking. idk.
the 'don't go beyond self defense' only sounds good in your head, when you are calm and logical. if someone comes at you, they want you to be hurt and if you only knock them down on the floor once, it will only make them more angry and just want to hurt you more.
If someone comes at you with the intent of harming you, beat the absolute tar out of them if you can.
They have no right to hurt you, the one body you'll ever get, and put your health at risk and possibly kill you. The act of attacking someone over something so stupid is the ultimate disrespect to your person.
I have one life, and someone attempting to hurt me and possibly end it by accident over fast food deserves every bit of the beating they receive.
The man being attacked did not get convicted of a crime for this situation, and I am glad he didn't. He may have gone a wee bit overboard, but you can't see if the two attackers are trying to grab for a weapon.