It looks like vipscasino.net belongs to another Linode customer and its DNS records haven't been modified in six months. Most likely, that customer misspelled their IP address, or their IP address changed months ago, they forgot to update everything, and the IP eventually found its way to you.
There isn't much of anything you can do about it -- you can't stop people from putting silly things in their own DNS records. You could write 'em an email, or something, but that seems excessive to me.
As for Nginx, even if you give your server block a name, when Nginx receives unrecognized names from clients, it will still use the first vhost as the default unless you configure it otherwise, by putting another vhost first, or using the `default_server` parameter of the
`listen` directive.
You could create another vhost that just does a redirect to your website or returns an error or empty 'Hello World' page or somesuch.