When a power throttling event happens it means that the CPU is consuming an amount of power higher than the power limit (and PL1 is, by default, the same as the TDP), after power throttling occurs the CPU is forced to work at a lower frequency so the consumed power doesn't exceed the limit, this is done to avoid overheating due to the system working at a higher power than the cooling system can dissipate. So power throttling is just proactive thermal throttling.
Undervolting a CPU will allow it to work at a lower power therefore it won't surpass the power limit, of course if you undervolt the CPU too much it won't be able to get enough power under intensive tasks and you will get a BSOD (or a forced CPU shutdown if you set the undervolt really low). But in this case there are no signs of the CPU misbehaving due to a low voltage so he can undervolt it.
TLDR: more voltage -> more power -> more heat so you want your voltage as low as possible