It seems that a moderator thought that it looked like the answer was within the thread and marked it as assumed answered. You as the original poster can override this by picking the actual correct answer within the thread. If there is no correct answer (as in this case) you can click one reply as correct and then click it again to indicate it's actually not correct. This sets the thread back to "Not Answered". A bit of a faff I'm afraid but I haven't been asked about this before so hopefully this is a rarity.
I've set your thread back to "Not Answered" for you. Please do let me know if you experience this again.
They're usually right in their reviews, so I don't think it's a big problem, but this one was clearly wrong so thanks for the tip.