Which group do you think it is?
They’re physically fit which implies they’re young people. That makes me think students, interns, rambunctous young leftists with a flair for theatrics and “direct action”, maybe Antifa. Seems a little too far out to be the feds, but who knows.
Antifa can’t maintain OPSEC so that nobody knows when and where they are going to show up. After the march, they slip away without anyone able to follow them. If someone did I’ll wager there would be some kind of interference by another group.
This is a tightly controlled operation by disciplined agents.
Students mostly doing the marching - the grunt work. However the organizing, direction & coordination could easily be supplied by activist Congressional staffers.