This is the truth. Aside from solar there are plenty of folks with backup generators that automatically come on whenever grid power fails. When maintenance crews came through my neighborhood to upgrade the old pole fixtures, they grounded out each block to keep any backfeed off what they were working on.
No, it's more than that, it's not just a safety feature that you could disable: the plug-in panels need an existing waveform to synchronize to, if the grid is dead they can't produce an AC voltage signal on their own.
We know how to make inverters that can produce an AC voltage on their own. It is not particularly difficult or expensive. The reason why we do not put those inverters in plug-in solar units is entirely because we don't want them to have that ability.
Those are a different design inverter than cannot plug into a wall. It isn't hard to design either type, but they need different designs in some critical areas. (you can design one that will do both as well, but it would be more complex)