It's not so much being unplugged as it is sensing whether the mains power is down. If it is, they stop backfeeding immediately, just like hardwired solar inverters do.

If this weren't done, there would be risk of electricution to anyone working on wiring in the house or on the utility distribution network.

And the panels synchronize to the grid's frequency; a generator doesn't have any logic to synchronize to the grid's frequency.

Skip to about 10 minutes into this video: https://practical.engineering/blog/2022/12/5/what-is-a-black...

Furthermore, the danger of backfeeding is if you do it in a power outage and you start to power your neighbors' houses. It'll overload your generator and create a hazardous situation for anyone working on the wires. (This is why you're supposed to install either a generator switch or interlock. I have one that only allows me to energize when my main breaker is turned off.)

Thanks. I would have asked Claude or something but I know so little about this topic that I wouldn't have been skeptical enough of its answer.

But how do they do it technically? Some countries require anti-islanding devices for grid connected solar, these are around $1000. That alone is much more expensive than the $300 plug in panels.