I'm wondering which overcommit strategy this example referrs to.

Because If my bitcoin price checker built on electron will start allocating all memory on the machine, then (assuming no overcommitting takes place) some arbitrary process (e.g. systemd) can get malloc error. But it's not systemd's fault the memory got eaten; so why it's being punished for low memory conditions?

It's like choosing a random person to be ejected from the plane.