That's fine, but for me, as long as there is a patch, the game is not finished as it still has content to play. Unlike when a game is truly finished, where there's nothing left to do in it.
The problem is knowing when the last patch will be.
I get your point, cause like you said it can cause confussion, especially for people who want to wait for games to be finished before playing them and suddenly see that more content was added.
But on the developer side of things, it honestly makes a lot of sense, cause that way you can... let's say "close the door" to a game, but without completely "locking the door", so you can start a new project or have a little bit of a break without the pressure of having an unfinished game (and the added pressure of players actively waiting for a new release), but you can still go back and make extra content when there's some new small story that you want to tell, and you can work on it in a more chill way cause you are not failing anyone for taking your time with it. This works better when the developer is pretty open about their mindset and development process, which from what I've seen is the case for this developer.
So honestly as player, I think it's best to think about these cases as "game is finished, no need to expect more", and just welcome the surprise when and if there's something new at some point. Maybe think about it as the indie games equivalent of DLCs in a good AAA game, as in you didn't need them, but it's cool that they came out.