Since your whole case appears to depend on there being no transients on the grid power lines in your neighborhood during an unplanned outage, tell us more about these "relays" that isolate your home from the rest of the power grid during outages.
When you talked about it early in the thread I, and some other posters too, thought you were talking about some kind of battery backup or uninterruptible power supply (UPS) system kicking in. If you're going to use a battery bank or generator to power your electrical panel during an outage, you need a relay or manual switch to isolate your home wiring from the grid, sometimes called a Transfer Switch. That would be your own property and located on your own premises (which would be the only way you'd be likely to hear any sound of "relays" due to the outage). Without such a device, energizing the wiring to your home's electrical panel will also energize the supply lines they're connected to, risking electrocuting people who are working to restore the power.
If you aren't using a transfer switch, then yes, transients in the power lines absolutely can occur during an outage, especially the first few seconds. And obviously did, in the case at hand. Some of your and/or your neighbors' lights flickered. That's what the video shows.