The McDonald’s employees have no obligation to break up fights or defend aid customers when they get into a fight.
This was an unprovoked attack on a minor.
However you are right they not only did not have any obligation to intervene but the way the system in the area is being run they would have likely ended up being arrested themselves.
Apparently the AG in the city of LA does not regard assault and battery a major crime as they have already reduced the charges to a misdemeanor.
Employees in nearly every enterprise are instructed to refrain from grabbing, blocking or hitting a suspect they see committing a crime in the establishment.
And we “have no expectation of protection from crime” from law enforcement officers as courts have ruled. Officers will interview people and make a record of the events told to them.
If any of us “take the law into our own hands” we will be sued and probably owe money in a settlement along with going to jail.