My understanding from the article is that the problem isn't that the price was propped but that they created fake tether to do so.

By fake, I don't mean the tether wasn't real, but that it was not tied to dollars.

So they claimed tether was tied to dollars but they produced a lot of it to buy up Bitcoin and the fear is that they didn't wait for dollars to come in but just made the tether out of... well, ether ... and used that to prop up bitcoin which they converted into actual wealth.