Giving a CPU more voltage is just what overclocking is. Considering that most of these modern CPUs from both AMD and Intel have already been designed to start clocking until it reaches a high enough temp to start thermally throttling, it's likely that there was a misstep in setting this threshold and the CPU doesn't know when to quit until it kills itself. In the process it is undoubtedly gaining more performance than it otherwise would, but probably not by much, considering a lot of the high end CPUs already have really high thresholds, some even at 90 or 100 C.