From a poster, who apparently was at JordanCon:
"I was talking to Brandon when he discovered the cover in the booklet and he said there is something very, very wrong with the cover. He said it's an error that, if you were reading the scene in the book, you'd flip the cover over and go, 'Hey, that's wrong!' He wouldn't tell us what it was, but he said he'd try to get it fixed before the book came out."

And another poster confirmed: "Brandon said there's something very wrong plot-wise with the illustration."

Maybe this mistake is that Noal isn't shown correctly. On the other hand, it simply might be something like that e.g. actually Mat is using the bronze knife to open the Tower of Ghenjei.