Because this is the whole .apk/game for the next version of Terrene, so it downloads a new app for people to play the latest version of my game. This is how Renpy for Android works.
As for starting again, like it is written in the install steps for Android before you download Terrene here on itch, with Renpy games/Android, you'll probably need to copy your saves over, if you want to use them, otherwise you'll need to start again.
(This is only if the old/new versions of Terrene are compatible though.)