1. He wasn't writing this, he was describing it on Donahue, during an interview. It is too long ago for me to recall if he was hawking a book, but I don't believe that he was.
2. There are a gazillion items surrounding us today that would have elicited a similar "fecal" remark 100 years ago, let alone 100,000 years ago. Just as a "for instance", contemplate strands of nanotubes, metallically sealed, perhaps in a honeycomb structure, perhaps bonded through a metallic core. Even if the strength of each strand was slight, imagine 10^15 strands. Might be quite strong, lightweight, and thin? But I suppose a bigger issue is that we cannot fly about as UFOs are described. But what about in 500 years? 10,000? 100,000?