You say something about everything grammar related. Then when challenged you gradually backpedal saying either a) It was style not grammar or b) I don't care. Nearly every post you make follows this pattern. It's grating. Pick a position.That was my second suggestion trying to better translate what she said. It's correct though because "controversy is a noun in that case, one may say a thread is "filled" or "contains" something.
The first suggestion is closer to what she actually said, with "controversial" describing what is being disputed, i.e. the "topic", by the people in the thread.
NO ONE is arguing over the actual thread though. Which is what the original sentence means.
You see where I'm going?