Oh Nigelar, you beat me to this answer...
In Android, Kodi is a separate application which can be installed and uninstalled any number of times like any other application.
But LibreELEC is is a tiny Linux OS built around Kodi. Both are integrated and can not be separated. LibreELEC being a small Linux, will consume small resources compared to Android. Hence it is very efficient and good for devices with low memory and slow processor. That is why we can have a LibreELEC Kodi on a Raspberry Pi.
When a new version of Kodi is released, the LibreELEC team will work on it and integrate it with Linux OS and release it as a new version.