Are you using risk aversion with a meaning other than “downward-concave utility function” by any chance?

Sort of. I was referring to ambiguity aversion, as you can see in the clarification in that very sentence. But I would argue that ambiguity aversion is just the same thing as risk aversion, at a different meta-level.

Though it might take an insane person to prefer a "certain 1/3 chance" over an "uncertain 1/3 chance".