Don't get me wrong, but this way of serving content has been common since, well, apache 1.2 days and mod_proxy ReverseProxy: CDNs did not bring anything new in that respect.
Basically, you are confusing some terminology and not really making any point: in your example, there is only one origin, that of example.com. Yes, servers can forward any data they wish to other web sites (like AnotherSite.com).
Sure, and a service that is able to scale much better, has a fatter pipe, allows configuration through a web UI...
But in this context, how does this matter? "Origin" is a client/browser side concept, and however you serve your website internally, it appears as one web site. Basically, I replied to a comment bringing CDNs into discussion where they are totally irrelevant.
Origin checks can't protect you against servers forwarding your data to a privacy-invading site (eg Google), and a server can do that simply by being a reverse proxy to another site.
Basically, you are confusing some terminology and not really making any point: in your example, there is only one origin, that of example.com. Yes, servers can forward any data they wish to other web sites (like AnotherSite.com).
What is the point?