Article: “The enemy force had “technical” vehicles — light, improvised military vehicles — and rocket-propelled grenades, the official said.”
Those technical vehicles are light pickup trucks mounting machine guns or guy with RPGs. Back during the war between Libya and Chad in the 1980s the Chadian forces used Toyota pickups and one nick name for the conflict was “The Toyota Wars”. see: https://en.wikipedia.org/wiki/Chadian%E2%80%93Libyan_conflict
Also, note that it was 4 US soldiers and an unknown number of Niger troops versus 40-50 ambushers.
“Technicals” are mean little machines. ISIS used them to invade Iraq.