The statement, which is attributed to the Marquis de Talleyrand, a member of the Directory, Napoleon's government, and the restored Bourbon government under Louis XVIII, is referring to the fact that Louis XVIII allowed himself to be influenced by conservative royalists in his government, including the future king and would-be absolutist Charles X. They had forgotten nothing in that they tried to restore the traditions of the ancien regime, particularly those pertaining to the power of the monarchy. They had learned nothing because in so doing, they ignored the aspirations of the liberals whose unhappiness had helped trigger the revolution that started the whole business in 1789. Ultimately, it lead to Charles's downfall in the revolution of 1820, when the "liberal" Louis-Philippe was installed as monarch. Most historians, I suspect, would agree with Talleyrand's assessment.