Your assumption that “Facebook’s algorithm is able to parse shared content, and looks at the author name on that content to see if it matches the name of the person sharing it” is spot on. You used to be able to query similar data for pages’ posts in FQL.

The old FQL stream table contained, for each post, the id of person who published it (actor_id) and the id of the news feed where it appeared (source_id). A typical query for posts would specify a source_id and then use the owner or others stream filter to get the corresponding subset of posts. It follows that Facebook would define a similar actor/source relationship between the author info in the og:meta tags and the owner of the profile/page on which a story appears.

Another possible explanation is that your friends are more broadly connected on the social graph to the 3rd-party articles you share than to your own. Perhaps other of your friends’ friends have shared the same 3rd-party content with them, but you alone are sharing your articles with them. I’m just speculating here, of course, but I’ve seen this effect before.