There is a single video but reports of multiple separate occasions in which it was done. The video was taken after the story had already broken on newspapers because the current Italian government officially raised it with France. Chances are that it had already happened several times, these things are usually kept quiet and dealt with diplomatically if they are occasional - unless one side is unresponsive and the abuse is repeated, which is probably what happened here.
TBH it's not even the most high-profile case, the stuff at Ventimiglia (where France simply blocks most migrants) is pretty egregious too. The Brits do it as well in Calais, but at least they had the honesty of not signing the Schengen treaty to begin with.
Please tell me you have a source for that.
/ Edit It seems to have been a singular occurrence where two migrants were deported unofficially by French officers.
Your phrasing made it sound like a regular occurrence of at least tens of migrants... But it is technically correct, I guess.