If that procedure leaves an unchanged old contextMenu.xml the installation is not correct at this point.
yes, you are correct.
the reason is, that the notepad++ installer/updater will not replace your existing contextMenu.xml.
this is by design and works correctly, as it would otherwise remove any customised context menu settings, every time a user makes an update.
note: you will always find two different copies of contextMenu.xml on an installed version of notepad++.
one at %AppData%\Notepad++\contextMenu.xml which contains user customisations, and one template at %ProgramFiles%\Notepad++\contextMenu.xml which contains all new changes of the latest update/install, allowing you to compare it to your personal contextMenu.xml.