"The API does not support retrieving blog posts by author."
If you add the code in debugger you will see that there is no author for the content item. The Author appears only for the blog. The Content items are associated with the blog ID( parent ID)
The last issue you have:
You should create Blog page where all posts will be visible. Then create a new page - say User's Blog. There drop Blog Posts control and filter the users by blog for the control designer ( step one). By doing so on this page you will have the posts created only from your "User". The same approach is used at http://blogs.sitefinity.com/
the Telerik team