But the government is allowed to track people's license plates. There's nothing against the law for a police officer to stand at an intersection writing down all passing car's license plates with a pen and paper. Flock is the same thing, just much more cost efficient.
This is not that
It is exactly that. These cameras are only recording cars on public roads (and sometimes e.g in the parking lot of Home Depot, but those areas are still in plain view).