Dude!
Standing up and turning one's back on the speaker amidst a seated audience is a standard leftist tactic and it most certainly is a disruption.
If you want to argue that it is a "small" disruption and that this makes it acceptable that is one thing. (I disagree that any deliberate disruption is acceptable, btw.)
But the plain, simple fact of the matter is that this protester was deliberately disrupting the event.
so standing quietly in a seated audience is disruptive? Did he get beat up for being a kook or not bowing to the queen?
I can see you will be useless in our cause.