You can buy them from unofficial sources if you're lucky enough to find one. The OP in that thread was offered one from and unofficial, small batch of AI cards and had to pay about 1.5 times what you'd pay for a regular 4090. The cards may very well be from a similar source to this one.
So "you can buy 2-slot 4090s" is technically correct, but isn't actually true for most people even if they had the money.
It's probably just you. The photos just look like they were taken with a mediocre cell phone camera. The background in the "guy holding the card" photo makes sense, which is from very hard to impossible to do with AI for now for such a niche subject.
Plus, we know blower-style 4090s already exist and can be gotten through backroom deals if you're ordering in bulk from the right place and can pay a lot of money. And there's a lot of demand for them. So there's nothing to fake.