That is likely an "ARC" (Advanced Reader Copy). Publishers send these to reviewers before the official release. They often have "Uncorrected Proof" stamped on the cover. These are rare but highly sought after by collectors.
After "The 100" TV show exploded on Netflix, viewers wanted to read the source material immediately. They didn't want to wait for shipping or visit a library. The instant gratification of a PDF on Google Drive satisfies that urgency.
Absolutely. Email the PDF to your Kindle's unique email address (found in Amazon account settings > Devices). Put the word "Convert" in the subject line, and Amazon will automatically convert the PDF to Kindle format.