The WordPress blog has a "pinging" feature built-in that notifies a pinging engine (which notifies Google) immediately when a new post is made.
Your friend's site is merely benefiting from the insight of the WordPress creators
SEO knowledge.
There are other plugins you could add to a WordPress blog to automatically create XML sitemaps & to notify Google of changes to them, but it doesn't come installed as a default, so your friend probably isn't using this method.