Yes, very good. This is the difference between "as a matter of law" and this case. Here, it looks like the aggravated assault came in because the attack did, as a matter of fact, endanger the life of the victim. Contrast the OP case, where it specifies that the victim's injuries were not life-threatening.
The judge may still have held that multiple attackers are aggravated assault as a matter of law, I'd have to read the whole case, but the judge could also have simply held that the facts of this case, viewed in isolation, constituted aggravated assault because the assault endangered the life of the victim.
The assault in the op just happened, and it has not been released what exact charges have been laid. Any mention of specific charges has been speculation only.
"Six accused faced five counts of aggravated assault. All six were charged with aggravated assault of the primary victim by kicking and beating him and preventing his escape; two were charged with aggravated assault of a second victim, and two were charged with aggravated assault of a third victim. The Crown witness's first-hand evidence about the assaults was supported materially by other evidence. At a celebratory fraternity party attended by all six of the accused, a pregnant woman and the alleged father of her child ended up in a physical fight on the street outside the fraternity house. The third victim attempted to intervene and help the woman and was assaulted and wounded by one of the accused and struck by two other accused. The second victim tried to intervene verbally in the dispute between the couple, and was assaulted by two of the accused. His injuries rendered him unable to come to the aid of the other victims. The primary victim went to the aid of the second victim and was surrounded in a circle by all the accused (including the Crown witness).The primary victim had done nothing to provoke his attackers but was knocked to the ground and kicked repeatedly in the head. As a result he suffered life-threatening injuries and permanent brain damage. One of the accused fled across the road and was followed by the remaining accused. Subsequent flight from the police was seen as further evidence of the consciousness of guilt on the part of the accused.The trial judge accepted the evidence presented by the Crown as having been proved beyond a reasonable doubt. All six accused were guilty of all 27 counts in the Indictment. The Crown witness was not pressured or manipulated into providing a statement to police, and racism was not a motivating factor in the attacks."
What is bolded would have been the reason for aggravated assault charges.
Here is the actual court documents, nowhere is it mentioned that the charges of aggravated assault was the result of multiple perpetrators, on the contrary, the judge specifically cites 268 and the definition within.
Also, the small section the you cut and pasted does not discount s21(1) but does the exact opposite.