In this case "taken aback" is a little stronger and hostile than "surprised," but it's not at all in terms of "I should get free food of my choosing." I'm not frustrated that a Holiday party on the other side of the continent isn't offering free food that I like. I'm frustrated that in a gathering of intellectuals who have dedicated their lives to rationality and the study of how to create AI that will, hopefully, be able to radically change the world, eating meat doesn't seem to have even registered as a bad thing with any of them. This does not bode well, IMO, on the nature of the hypothetical utopian future I might look forward to.

(It was later pointed out that the menu DID include vegetarian things, but those things were all things I'd consider obviously a "side dish" as opposed to a main course. Other vegetarians might disagree with me on that, and if that was the intent of the organizers, than I do apologize. But when the subject was brought up in that thread it didn't seem to be)