Russian soldier shows fields covered in fiber optic wires from Ukrainian drones.

Which is significant how / why?

Ukraine has had a lot of success using remotely operated suicide drones. They are cheap, built mostly from off the shelf hobbyist grade components, but with a few inexpensive upgrades the signal goes for miles. Strap a grenade on the bottom or any kind of bomb with an impact fuse and you have an excellent remote control weapon.

So of course the Russians start deploying radio jammers to block the drone signals.

The solution to this is fiber optics. The drone carries a giant spool of hair thin fiber optic cable which sends control commands from the operator and video back from the drone. Because it's a cable, it's immune to jamming.

The cable is insanely thin, usually in the tens of microns thickness. So they don't bother recovering the cable, drone flies out spooling out cable behind it, hits its target and blows up, operator just detaches that fiber and pulls out another drone with another spool of cable to start again. This leaves tons of little fibers laying around on the countryside because every drone leaves one in its path.

That's the point of this video. Most of those fibers have a dead Russian soldier at the end of them.

This link explained a lot for me

https://defensefeeds.com/analysis/how-do-fiber-optic-drones-work/