How come my first blog post and my home page have the same title?

The “Reading Settings” at a domain’s wp-admin/options-reading.php is, by default, set to latest posts. So, WordPress, by default, would show the title of the post being set at “General Settings” at a domain’s wp-admin/options-general.php . In this case, Yoast’s WordPress SEO plugin would have form fields to customize it.

When the “Reading Settings” are changed to show a static page as the front page, then the title of that page is shown as the title of the blog itself. This is the expected default behavior. Yoast’s WordPress SEO plugin would have not any form fields, in this case, but would contain the link to the post to edit the title and the description.