It's exactly the opposite of a scam and you are stating why: the developers do not hide what they are doing. They are updating that info daily, and all those progress charts are kept on their public discord server, so people only need to check them to see how fast they are working. It's so obvious that things are going slow that no one with a half-functional brain can feel cheated about the development pace - frustrated? absolutely, but not cheated. People can also know how much money devs are earning, as it's also publicly available on their Patreon page. If someone chooses to pledge, is because he is fine with that, not because he's being misled into believing that the update is going to be released soon or devs may be running short of money. And those unhappy with how things are progressing only need to hit the unsubscribe button, which is as easy as hitting subscribe -and they'll still get the game for free whenever it's ready. That can't possibly be a scam.
Because the actual amount of what they call 'bugs' (you can find the description in the 'FAQ' section in the OP) can only be properly estimated once the planned content is ready. When they start any development cycle, they are aware of a few bugs from previous chapters, and then a few more get added during development as people report them or devs notice them while coding and testing parts of the new content. But it's only when everything is put together that they fully focus on looking for all the things that wouldn't work in a full build after that new content is added - which is why the bug tasks took such a bump after content tasks got to (almost) 100%.
You can think of those 'bugs' tasks as a second pass (and third, and even fourth if necessary) to make sure the 'coding' tasks were properly done: i.e., they initially added a coding task to indicate the MC needs to start a quest during the first evening at his tent after meeting a certain character; then, when they have this coding task completed and all the art and dialogues have been added, they test the full game from scratch and find out that, for some players who may choose to play the available quests in a different order, there's another quest blocking this particular scene or taking precedence when it shouldn't, and that means a bug task needs to be added. Sometimes they detect those issues while still making the planned content and update that bug count during that phase, but sometimes it's just impossible to detect them unless you start a new playthrough, or devs are just too short-sighted and don't realize those possible conflicts before it's too late. That's standard game development.
And, if you take a look at the most recent progress trackers, you'll see that these days they are mainly completing 'edit' tasks (that is, fixing art and dialogues, as stated in their message), because it's only after having those fixed when they can properly test the game again and focus on fixing actual 'bugs'.
No, it's not a deception. All those tasks they keep adding, everyone can learn about them first thing in the morning -not just patrons, but everyone. So no one needs to subscribe to find out, and that's exactly the point of making that tracker public: to let everybody know how things are progressing, as stated above. On top of that, and in case these numbers weren't explicit enough (because, as some comments I've seen today about the % of progress show, some people have serious problems with Maths even if they have 'math' in their usernames), devs keep saying the update won't be ready *soon*, but in a few months. Again, clear and transparent info so people can make informed decisions about supporting the game. Even if someone were so financially stupid to rush and pledge based only on the false assumption the game was about to be released (and anyway I wonder, why would anyone do that instead of waiting a little bit more until the game is actually out?), devs quickly stated in several public comments that we are still some months away. And this last time they even described what they are currently working on.
If they think the game needs that extra month, you can be sure they'll take that month. And fear not, everybody will know about it as soon as possible and without paying a dime for that info.
You can be frustrated, and you can not believe what devs say, but, so far, all their statements check out using fair logic. However, most of what I've seen here in the last months is exactly the opposite: twisting logic (or blatantly making false statements) to support prejudices and unmovable opinions against these devs and their supporters. It's a sad mix of frustration, jealousy, and pure trolling and brigading from self-righteous people who can't accept others freely spending their money how they see fit -or maybe from people who simply get off on collecting reactions from their online 'friends in hate' that keep patrolling the thread.