In the US we call that "silt fence". It is used on construction sites for a variety of erosion control purposes, and indeed the Youtube video description reads "As the helicopter began to take off following the hover, it traversed a grassy area adjacent to the ramp about 10 ft above ground level, where a silt construction fence was obscured by tall grass. As the helicopter overflew the fence, it became unsecured, blowing up and into the helicopter’s main and tail rotor system."
I wasn't there, obviously, but I'm betting it was clearly visible to the pilots and not at all "obscured by tall grass". It looked like it was protecting against erosion along the edge of the construction area, which is not unusual at all. Sometimes it is placed vertically on stakes. Other times it is stapled down to the ground with long turf or ground staples. Sometimes it is held down with sandbags.
That said, an easy thing to overlook, particularly if you had already overflown it without incident.
Scary stuff!