I remember reading the same thing, and iirc they were right. The subcontractor builds the fuselage and delivers it to boeing.
Boeing then opens up whatever doors and plugs will make it easier to install the interior. Once the interior is installed, they're supposed reinstall and secure all the doors and plugs. Because Boeing is going to be opening them all up, they don't bother to fully secure them.
That said, it sounds like a process that's just asking for miscommunication. If you expect the part to be removed, just deliver the part separately. If you put the part in it's place, then fully install it and secure it.