Very interesting.
There is an excellent Wikipedia article on FRBs
https://en.wikipedia.org/wiki/Fast_radio_burst
Over a dozen of these events have been detected over the last few years, too many for them to be of artificial origin (IMO, but who knows?) It seems unlikely that many extragalactic travelers are using this form of propulsion, spread out over so much space and time, and we are detecting the artifacts, But right now, the light sail explanation is as good as any.
OTOH, I am comforted by the idea that astronomers still include ETI in their speculations. If we ever do find THEM, it will probably be through something like this.