And yet, it wasn't Demon's Dance that killed Joffrey. It was the strangler.
As for flavor text, the text does not always reflect the card. One of the Pycelle's (I think TfR) actually quotes Tyrion Lannister. And a line may be taken completely out of context for the card, yet the words by themsevles fit what the card conveys.
Personally, I just can't buyt he arguement that the game needs to avoid spoilers of what happens in the books. Sure, some spoilers are huge (Eddard, Jaime's hand, the Red Wedding), but by shutting out these events we are limiting the options of the game. Yes, some people are going to have something spoiled by a card (whether intentional or not), but if the game decides it is never going to create a card that spoils an event in the books the game will suffer. I know when Five Kings was released I really, really wanted a Euron with a King trait, and I got it. But that would spoil the end of the Kingsmoot. And seeing Renly and Stannis with King traits lets us know that something happens to Robert (oh, and Robb Stark with the King trait instead of Eddard is also a clue).
But, as you also pointed out, you can misread a card into believing a spoiler. So it can balance out that way.