The video we're discussing talks about how it's an "achievement" for chickens that there's 23 billion of them at any given time, making them by far the most populous bird species. For comparison the red-billed quelea is the most populous wild bird species, with around 1.5 billion individuals.
So the question if you're going to pose an ethical conundrum isn't to suppose that all 23 billion would otherwise be living happily in the wild, but rather the antinatalists argument that chickens would be happier as a species if they were all dead instead (well, except maybe some low number of millions who'd make it in the wild).
Of course it's rather hard to have that conversation with a chicken. Assigning human motivations to animals of that intelligence doesn't make any sense. Would you rather spend your life as a bird eating trash from a landfill, or take your chances in the open skies?
We know what most humans would pick in that scenario, but we can also see that there's wild seagulls that voluntarily choose to live their whole lives doing not much of anything except eating trash in the same small place, and they're pretty intelligent compared to chickens.
As ethical trolley problems go comparing the intelligence of a single chicken v.s. a single cow doesn't make sense either, as you need a lot more chickens to produce the same amount of meat.
If we're going to suppose some linear no-threshold model of cognition for farm animals we'd thus be better off if we killed 100 human-level intelligence animals if they were so large as to give us the same amount of food as those 23 billion chickens. After all we're killing a lot more humans than that yearly just from exposure to a chicken population that large, nevermind the ethical calculus.
1. https://en.wikipedia.org/wiki/Red-billed_quelea