English is not peb's first language, and as far as I can see (not my favourite subject) he has the correct interpretation of the situation, so no implied criticism, but he meant "overboost".
The reason this answer is correct is that the waste gate allows exhaust gas to bypass the turbocharger to keep the boost correct. If it sticks closed as the aircraft descends into air of higher pressure the effects of the turbocharger will increase the pressure by as much as it was required to at higher altitude. This may be more than the engine can cope with.