Actually, the story of the Anunnaki does come from the Sumerian clay tablets. There is some controversy as to whether Zecharia Sitchin translated those tablets, or got the story from other archeologists and linguists who translated them before him. But that's not important to answer your question.

What Linda read in those government documents goes farther back than the Anunnaki. In fact, it is said that the Anunnanki did not create us, but rather genetically modified us. We were already here as a result of other experiments conducted by other alien races going back millions of years. It is one very interesting rabbit hole to dive into!