Oh, I don't know if that's completely correct. For many years the Saudis supported radical Sunni mosques all over the west. Whether or not the predominantly Saudi hijackers were from a particular radical group supported or opposed by the Saudi government, there is historic responsibility for the promotion of radicalization by the Saudis.
No doubt the Saudis support Wahabbist Islam, which is radical.
But the AQ claims are complete bunk. The Saudis have been torturing and executing and imprisoning AQ operatives for many years prior to 9/11.
They wanted to overthrow the Saudis. They are mortal enemies.