This is of course untrue. While he stabs the first Sentinelese with his sword, the others could rush him down and immobilize his limbs. Or if they wanted to avoid any casualties they could pretend to surrender and then wait until he falls asleep before immobilizing him. Or if they don't even want to pretend to surrender, they could tire him out just by continually retreating every time he tries to advance, as it will fatigue him more to move in armour than it will fatigue them to move without armour. Especially considering the local air temperature.
Then they could cook him alive inside his armour.