I see in the video, they say they "believe" the mass grave contains British and Zulu warriors. Could possibly be just Zulu warriors, as we know many of the dead Zulu's were lay to rest in grain pits.
“Wet With Yesterday’s Blood” by Ian Knight
"By late afternoon, the great army had begun to retire back towards the Ngwebeni valley, where they had started the day, carrying their loot and their wounded with them. Friends and relatives of the dead dragged many of the corpses into the dongas which flow below the present site of the St. Vincent’s mission, and covered them over. Other corpses were simply left with their shields covering their faces in token burial."
"Meshla Kwa Zulu:
The dead Zulus were buried in the grain silos in two kraals; some in dongas, and elsewhere. Zulus died all round Isandwhlana.