The install guides for the OnePlus 2 and the OnePlus 5 used incorrect terms to explain installing the updates in the Recovery mode. This happened, because I don't actually own these devices. Instead, I had based the guides around information present on the internet (in 2016). That information seemed to differ with the current version of the recovery mode.
As I'd like Oxygen Updater to be easy and straightforward to use, I have corrected these guides to match with the current version of the Recovery Mode present on these devices.
What does this mean for me?
It should now be easier to follow the install instructions when installing an update on a non-rooted device (or installing an update manually on a rooted device), because the terms of the guide exactly match with the those present in the recovery mode screens. If you are using Oxygen Updater version 1.1.0 or higher, you don't have to update the app to receive the correct instructions. These are automatically downloaded from the internet when you open them. If not, update to the latest version of Oxygen Updater using the Google Play Store.
What about the OnePlus 3 / 3T?
The OnePlus 3 and 3T are not capable of installing updates via the Recovery mode and use a different install method, available within the standard Settings app (called Local upgrade). The installation guides for these devices will be checked soon and corrected if needed.