"Every perception is to some degree an act of creation, and every act of memory is to some degree an act of imagination."
-- Gerald Edelman, Second Nature: Brain Science and Human Knowledge
1 More patterns of Anki use3 More patterns of Anki useMore patterns of Anki usePart I: How to remember almost anything: the Anki systemAugmenting Long-term Memory2020-09-24Journal
I'm not sure what's responsible for this effect. I suspect it's partly about focus. When I made mistakes with the combined question, I was often a little fuzzy about where exactly my mistake was. That meant I didn't focus sharply enough on the mistake, and so didn't learn as much from my failure. When I fail with the atomic questions my mind knows exactly where to focus.
In general, I find that you often get substantial benefit from breaking Anki questions down to be more atomic. It's a powerful pattern for question refactoring.