Interesting. I was thinking that it might be a pathogen/parasite. If it’s simply a behavioral thing that’s good to hear, but it doesn’t appear to be directed at other fish.
It's difficult to determine from such an abbreviated video, but the situation doesn't look too serious.
As long as the fish continues to eat and otherwise is acting normally, likely no worries.
If the twitching persists, you might try "Microbe lift Herbtana". It's an
anti-parasitic product, not too harsh, but effective.
Agree.
If it was a parasite, they'd be glancing (rubbing against objects in the tank.
And even though they are just juvies,a dominance hierarchy can be established early.
I also agree. My one of the fish in my breeding pair does this as well. I can't tell them apart so I'm not sure which one does it but I've seen it a few times.