[ak217]

This is just plain wrong. The poster didn't say they were at a standstill but that they had the brake pedal pressed. That means the engine could have downshifted into 1st gear and started to rev noticeably. The engine would also produce more power (and sound very different) when taking up load, even under the same RPM. Finally, as the other reply pointed out, the engine can spin a clutch or CVT.

[dx034]

The poster said that the brake was fully depressed with around 100kg of force. It won't take long for that to be in a standstill. And there's no way acceleration can overpower that kind of brake power. The sound might be scary but it won't change much about brake performance.

[jacobush]

Bad clutch plus bad brakes (but not so bad as to be unserviceable in light, normal use). Story is not implausible.