According to an article in the
New Indian Express, the American do-gooder inquired of the interpreter as to why the captors seemed to be angry.
The article says, "The video showed Michael Sharp and Zaida Catalan surrounded by seven people speaking Tshiluba, the main language of Kasai, armed with machetes, sticks and one with an old gun. Through an interpreter out of shot, the armed men promise to show the location of mass graves in the bush. Seemingly worried, the white man asks the interpreter in French with a marked accent: "Why are they armed and angry?" The two foreigners are quickly forced to sit on the ground before orders are barked and they are shot. One of the victims is then beheaded."
They're both walking in bare feet, though I presume their captors forced them to remove their shoes.