It's not hiding per se. It's more like it's dynamically publishing.
Think of it like this. Have you ever integrated Adsense onto your website? Do you manually add all the images and animation on your site? Or do you simply embed a JS code that dynamically inserts relevant ads on every users browser? That is exactly what is happening here.
The website (12up) embeds a Wazimo widget. Wazimo is a display publishing supertool from Israel. They're owned by Minute Media.
Wazimo allows you to publish, aggregate, embed and even integrate with ad services such as Google, Criteo and Mediavine et al. Think of it like WordPress on steroids.
If you want to see the rendered page, right click on the page and goto "Inspect Element".
When you send a view-source command - the code rendered is as it is received from the server (which is why you see nothing in this case). When you use inspect element, the browser shows the content after any DOM manipulations by the browser.
