The probable reason they used an error handler for that "welcome" page is so that it would keep /var/www/html empty and any upgrades wouldn't try to replace an

The probable reason they used an error handler for that "welcome" page is so that it would keep /var/www/html empty and any upgrades wouldn't try to replace an index.html or whatever you put there yourself. So it's a "hack" to serve a welcome page from outside the default DocumentRoot, not to force some kind status code. That status code is just a downside of this hack and not really of importance because whoever made it also knew it was going to be the first thing you remove when you want to use the webserver.