Smart switches, both dimmers and switches, will leak some voltage. I don’t know the in-depth details of why that is, I just know that they do. Some LEDs have a very low voltage threshold. So when LED stays lit, it’s probably not ghost voltage, it’s leaked voltage from the switch/dimmer.
When you use a bypass in a non-neutral situation, it’s there because not enough current is being passed by the bulb to make it back to the dimmer to power it. But that’s not the only use for a bypass.
When you have a neutral configuration and leaked voltage is causing a bulb to remain lit, you can either try using another bulb or install a bypass. When you install a bypass in this configuration, it will draw down the leaked voltage hopefully to a threshold below that where the bulb with light. It is becoming more and more common that bypasses are used in this fashion.
This thread is a good example: