Murder implies intent. Did they intend to murder him or were they just expecting to lay a beating that would hospitalize him for a few days?
I agree that it’s murder, but you can’t call it that unless you can prove that was their intent, as opposed to simply going too far.
That’s how the law works. You have to include the thought as well as the actions to determine proper charges.
From that video (and video never tells the whole story, granted), it seems to me that a jury could easily infer intent, and the requisite “malice aforethought”, at least for the more aggressive members of the mob.
For the others, who were participating in a felony (assault with a deadly weapon, in this case a “shod foot” as the police reports say), felony murder absolutely does NOT require inent. Mere participation in the underlying felony meets the legal elements of the crime. Would a jury convict given the ages of the offenders? Maybe not, but that’s a different question.