Line Lock with Drum Brakes ?

You missed the point. He was trying to claim that if it works foot braking, and not with the line loc, that there is nothing wrong with the brakes. But foot braking, he has four brakes. It proves nothing. Foot braking BOTH FRONT AND REAR brakes are active. Of course they hold better.
Unless it's a bootleg rear doing a one-wheel-wonder burnout, the rear wheels are both spinning & driving the car forward, it ain't the brakes.