relax... you read one 4 paragraph article discussing a situation about french secret service learning of a possible plot by islamic radicals to hijack a plane, in the year 2000.
Maybe you didn't notice but there was a big subheading at the bottom that reads "Specifics Unknown". Give it time for this to develope more.
But to tell you the truth, there are terrorist cells planning bombings and hijackings all the time. This may have been something completely "normal". And if the government was really confident that france was withholding crucial intel about 9/11 before it happened, I can assure you it would be viewed almost as an act of war in itself, and make them just as responsible.