What are those two lights in the sky in Army of the Dead?

In the opening sequence of the movie Army of the Dead (2021), we see two light dots in the sky that just fly off the screen at an enormous speed as the Four Horsemen convoy is leaving the base. What are they?

The two lights reference Area 51 and aliens

They are subtle orbs added by the VFX team as a nod to Area 51 and the film's alien themes. In the behind-the-scenes feature 14 Things About Army of the Dead, Netflix explains:

In the opening sequence, the VFX team added some subtle orbs to the sky as a nod to Area 51.

Director Zack Snyder has since gone into more detail about the zombies' alien origins. During a fan Q&A on Day 1 of Netflix's Geeked Week event (relevant article), when asked whether the zombies' blue blood meant they were robots, Snyder said that wasn't necessarily the case:

The robot zombies when you kill them, they spark instead of bleed. But the blue blood zombies – or the baby zombie when you see his blue essence sort of fade – I think it has something more to do with their alien origins than them being possibly robots.

He expanded on this in an interview with MovieWeb:

I had the idea from the beginning that these zombies were going to embody an evolution, that they were on their way to becoming something else, not stagnant like the zombies we're used to. It was a way to make them fresh, while still delivering the zombie canon in some ways. I really wanted this sort of weird ambiguity to their origins – which, of course, we'll explore in the animated series. If you pay close attention, there's a number of zombies that are clearly not zombies. You see normal zombies and then you see some robot zombies. Are they monitors that the government has placed among the zombies to monitor them? Are they technology from the other world? What's happening there?

Snyder went even further; in an interview with Total Film, he revealed that Army of the Dead and his sci-fi space opera Rebel Moon share the same universe, meaning aliens really do exist in Army of the Dead:

At one point in the show, they go through a portal into another dimension, and there are characters in that other dimension that they come across. In Rebel Moon, they’re in this bar, and one of the aliens is one of the characters from the animatic. So it’s definitely a shared universe.