How does Mechanical Turk re-load page content after inner-frame re-load?

On Mechanical Turk, it allows you to give a URL for the site to embed. For example:

http://ift.tt/1Kh6gI1

After a user submits the iFrame form data (with action = http://ift.tt/1yZNenw), it reloads the iFrame and it changes information on the Amazon page (the outer frame, which contains the iFrame).

How is this done by Mechanical Turk? How does the submission of the iFrame trigger an event to re-load the outer page with new data?