That's for sure a springtail. I'm sure you know this but for others reading, they're harmless.Video shows the big fungus gnat larvae squirming around and the 3 tiny ones fighting over scraps at the bottom of the tray in collected runoff.
You may notice a little white guy wiggling back and forth right above/over top the larvae.
It's not chewing on the larvae. Its actually at surface and would be the springtail. Only thing I can think it is due to its behavior and description as well as size and appearance. They are ghost white and look like they have little antenna on their heads.View attachment 856684
Those damn fungus gnats are mostly just a nuisance too. I've found them to be pretty much impossible to get rid of once you have them. Imid is about the only thing that will totally wipe them out but I would never recommend using it just for fungus gnats. Better off just putting a ton of sticky traps over the soil.