This isn't from Google, but it's a reliable source:
Subdomains are finally getting the same treatment as folders by Google | Fathom SEO Search Engine Marketing Blog
You would be correct... sub-domains are now being considered part of the same site. Essentially, the sub-domains' links are going to be considered internal (rather than external) links, which might hurt some larger websites.
It basically encourages websites to get more inbound links from external sources.