[0xricksanchez]

You're right with your assumptions! If you go to part 3 pretty much to the bottom of the article there's a good summary of what fields are included in their firmware verification headers.

TL;DR: They verify the length of the encrypted and decrypted firmware as well as multiple RSA signatures.

As much as I like pushing security vectors on embedded/IoT devices... This approach of obscuring what is being pushed in an update may not be the right approach imo.