Lexel is correct, the PCB is not metal core. You can make metal core PCB with via but usually the core is pre-drilled with bigger hole and backfilled with dielectric, then redrilled and plated (one of many ways). Doing your own diy with metal PCB has huge risk of shorting at the core/copper boundary, and with powerful lithium cell inside flashlight, can be a very bad result very quickly.
True, I meant similar idea.
There is risk with metal core boards but if done carefully can be fine.