Maybe they brake automatically - “regenerative braking”? I remember when I was test-driving Model S, the driving experience was very different from an ICE car, because as soon as you took your foot off the pedal, it started braking quite noticeably. To get an equivalent experience to an ICE car, you had to keep the pedal pressed ever so slightly (or change the settings).

Maybe regenerative braking is also when the brake lights turn on.

Yes you can coast normally if you disable regenerative breaking. If its on, your car slows down a lot faster than it would if you were just coasting, so it triggers the break lights when you remove your foot from the gas

It may be, I ride the accelerator so it doesn’t often trigger the brakes unless you let off by a lot then the regenerative braking really kicks in. So if you let off the accelerator enough it triggers the brake lights because the motor is “braking” and charging the battery.

Maybe... there's some kind of threshold of deceleration that triggers the brake lights when pulling off the throttle but I don't know what it is. It could also be autopilot on.