I does not sound like in this situation the shove was justified, but I have witnessed situations were it was.
One that comes to mind was when my kids were doing their 2nd OW cert dive. I was along as an observer / "unofficial DM", and acted as a 2nd set of eyes.
Anyway, during this particular dive a "vacation" diver got mixed in amongst the class, and was a "flailer" (used arms to swim underwater). He was essentially oblivious to his close proximity to the students, hit one in the head with his fin, and with his big sweeping arm strokes was a real risk of hooking a regulator hose on one of the students.
The instructor tried to get between his class and the offending diver, but could not get his attention, and moments later as the diver once again got close to the class the instructor swam up to him, and gently but firmly grabbed the diver, spun him to make eye contact, pointed to the class, and signaled for him to stay well clear.
Now, if a casual observer had only witnessed the instructor grabbing the diver, it would have looked a lot like the situation reported in this thread. But when the whole situation was observed, what the instructor did was reasonable.
After the dive, the instructor did talk to the diver and explain his actions, and the diver was not upset, and did understand.
I'm not saying the situation in this thread was justified (it does not sound like it from what was described), I just wanted to point out that situations can occur that to prevent a dangerous situation may require being physically grabbed, shoved, moved, what have you.
Best wishes.