They used freely available NASA data to map Russian and Ukrainian electronic warfare systems. The jammers used leak into the 1.4 GHz spectrum, which is suppose to be silent, and does so which sufficient power that you can be pretty sure it's man made.
So if you're looking for an intersting target, you could do worse than those lit up areas.
Small correction: the jammers used are specifically targeting the L-band, because it is used for navigation and satellite communications.
Normally ground transmitters in this band are using just a couple watts or less, so they don’t significantly impact the readings of a satellite looking at a large area on the earth, but a jammer uses a lot more power and can be noticed.
So if you're looking for an intersting target, you could do worse than those lit up areas.