"Does the author mean that the works that existed before he had been hired were protected by HIS non-disclosure agreement?"

Yes. He joined the firm and signed a Non-Disclosure Agreement. As he explored the firm's existing technology, he found some very interesting things, but he isn't going to tell us about the details because he thinks that his NDA covers IP generated before he started in addition to what is produced after. (He is probably correct.)

He is comfortable giving a broad brush description ("it was essentially human specified.")

"Does the author mean that the works that existed before he had been hired were protected by HIS non-disclosure agreement?"

Yes. He joined the firm and signed a Non-Disclosure Agreement. As he explored the firm's existing technology, he found some very interesting things, but he isn't going to tell us about the details. He thinks that his NDA covered intellectual property generated before he started, and even though he no longer works there, he is still bound by it.

He is comfortable giving a broad brush description ("...it was essentially human specified.")