I’m not an expert on Facebook sharing, but I’m pretty sure (not 100% positive) if you have a meta description that exists, that is the first thing it will try to pull. — http://www.bloggersentral.com/2010/11/facebook-share-shows-wrong-description.html
By default you have no meta description. This is something you’d need to add by using an SEO plugin like Yoast SEO for example. Aside from Facebook, it’d be a good idea to be using a plugin like this to attach meta data to your posts, anyway, for SEO purposes. — http://wordpress.org/extend/plugins/wordpress-seo/
Does that make sense?