There's a good explanation by Adam Engst in two articles over at TidBITS: Explaining Sierra’s Optimized Storage and How to Turn Off Sierra’s Optimized Storage. That Manage Storage window you got to from About This Mac is designed to let you turn on various Optimized Storage features, but not really useful to check their status or turn them off. Optimized Storage isn't a single feature you can turn off in a single place it's a bunch of similar features that you'll need to check and (if necessary) turn off individually.
