Open two windows, one with an outliner.
In the outliner, choose a document.
R.click > Open > in Left Editor Ctrl+Shift+Return
actually opens in right editor, whether using menu or keystrokes, and similarly, the request to open in the right editor uses the left.
This is true whether the outliner is in the left or right window. I have not tested above/below.
When an outliner is open in a single window by itself, the Open options in Editor and in Other Editor work.
EDIT: when I swap editors (View > Editor Layout > Swap Editors), the menu is correct, so maybe my report needs to include “swap editors” before the problem appears.