You are not wrong, just for Android. Sometimes. I don’t know why it’s working fine for OP.
The battery controller will reboot it after a second or so if battery voltage is too low, in this case zero. But only if the BMS is actually plugged in, if it’s not it doesn’t care (at least for me) and then it’s Android’s problem. Unless you are booting something non-Android, then it just works and shows 1%. Unless the load is too big for your charger to handle, lul.
Qualcomm SoCs specifically need to run without a battery for EDL/firehose at the factory. And for the devkits. Mediatek needs it for it’s own flashing thingamagig.
Fun fact, plugging in a charger to a dead phone/tablet/whatever doesn’t start charging right away, it powers the CPU from the plug for it to then boot enough to turn on the charger. Unless it’s wired shitily, then it just sits there dead.