I think there is a substantial difference though. Meat processing is done in a measured, considered way for a benefit (meat) that cannot be obtained without killing the animal. It is done in isolated facilities away from people who find the process disturbing. Just because people find something gross doesn't mean it shouldn't be done - we have sewage maintenance done out of the public eye too - but it does maybe mean it should be done where people don't have to see it. The only benefit this man gets from killing the animal is some sort of "revenge". But this is in principle completely contradictory to meat processing, where animals are seen as less capable of higher order experiences and therefore more acceptable to kill. To seek revenge, you would need to be assigning more higher order experience to the seagull than we typically see it as having. You have to see the seagull as selfish, stealing, criminal, rude, etc., even though in reality a more reasonable person understands that it's just an animal looking for food. Meat processing is not done out of some emotional vendetta against the animals, rather it is the cold detachment of it that is exactly what makes it acceptable. Can you imagine if we killed the same amount of chickens every day, not to eat them, but just because we hate them? This is much more horrifying! Because that would mean we think chickens are having complex enough inner experiences to warrant hatred, yet still we kill them.

Meat processing maybe isn't great, but it's still much better than this seagull killer. It isn't impulsive, it isn't disproportionate in response to the situation, it acknowledges and conceals its own horrors; thereby paying respect to important social codes. The actions of this man, though, disregarded the well-being of children and others around him, in an impulsive and disproportionate response - your average meat-eater is indeed better than that, I think. When I have a craving for some meat, I don't drag a calf down to the nearest playground, cut it in half and spray blood over the children, and proceed to mock the calf's weakness and inferiority as I beat it to tenderize it before consumption. I just want some food, dude. But what's this guy's beef? It's not beef, and it's not even seagull meat, but rather some frightening notion of swift and decisive revenge, which reveals that he is just waiting for any excuse to get away with brutalizing things around him.

The point is the it's not cognitive dissonance, it's just reacting to a different aspect of it than simply the dead animal.

Boy don't try that vegan crap on us, meat is faaaaaaar more nutritious than veggies.