[Governor Dinwiddie]

I don't know how they do this. It is generally wrong (perhaps illegal?) to backfeed electricity through a receptacle.

[Governor Dinwiddie]

The reason is because linemen or technicians on that line could be electrocuted. This generally requires a disconect switch from the mains.

[WhoisAlanGreenspan?]

According to the video its called 'grid following inverter logic', something like you and I might relate to as similar to pulse wave modulation; useful in electronic devices that convert direct current (DC) into alternating current (AC) by rapidly switching semiconductor devices like IGBTs or MOSFETs on and off.

Grid-following inverter (GFL) logic operates the inverter as a current source that synchronizes with the existing grid voltage and frequency rather than creating its own. The core control objective is to inject specific active ($P$) and reactive ($Q$) power by modulating the output current vector to match grid setpoints.