Watched the video three times, I don't see "flashing" lights. I'd describe them as flickering, then burning out. That mean pyrotechnics of some type, almost certainly on drones.
The formation appears to be an attempt to give the impression of a large V or triangle shaped craft. Looks like the pyro on the middle drone on the left ignited before it was aligned to form the leg on that side. If you continue to watch the video, you can see it is being flown toward the spot to align with the others, but they start burning out before the V is formed.