It's a good question, because I would say it's mostly not satire. It's kind of making fun of the perspective of thinking meat is unimpressive, but that's not exactly a view held by anyone except in the fiction of the story. I think toward the very very end tonally it veers close to a satirical vibe but it's hard to put a finger on what about it counts as satire strictly speaking.

I think basically the humor is how unimpressed they are with a Sagan-style sense of wonder at the cosmos that is implicitly treated as the human perspective, how bleak it would be if true. The aliens ridiculing that is funny, and the actual bleakness of it is funny too.

> What is it satirizing?

I think it's (partly) satirizing how we feel about ourselves as the apex beings, and as explorers of the cosmos and colonizers. What if we are actually quite subpar, and the actual apex beings in the universe find us so unlikely and disgusting that they prefer to pretend they are not there, thus giving an answer to Fermi's Paradox? They don't want to conquer us, they don't want to have anything to do with us!

But of course, it's also satirizing this alien-as-a-bug idea, so common of early scifi, that the alien is a disgusting mess of antennae or simly appendages. What if we were disgusting to enlightened aliens?

What we can absolutely be sure of is that Bisson wasn't making fun of meat or the human brain, the thought that apparently irked the topmost commenter.