According to AAM, in the single selection case, selection follows focus. See here:
https://www.w3.org/TR/core-aam-1.1/#h-mapping_events_selection

This means that the selected state should be set for focused items in a container.

This is really due to legacy. I'm not sure following the spec has a lot of value other than making us more compatible with Firefox. It actually is a bit annoying in that it causes NVDA to read "selected" for every gridcell.
 

According to AAM, in the single selection case, selection follows focus. See here:
https://www.w3.org/TR/core-aam-1.1/#h-mapping_events_selection

This means that the selected state should be set for focused items in a container.

This is really due to legacy. I'm not sure following the spec has a lot of value other than making us more compatible with Firefox. It actually is a bit annoying in that it causes NVDA to read "selected" for every gridcell.

Note that if we do this we should make sure that aria-selected="false" overrides the automatic behavior, because some single selection widgets support no selection vs focused item is selected.