The page also demonstrates how to only enable (or show) the Taler option if Taler is actually supported by the browser. For example, if you disable the Taler extension now, the Taler payment option will be disabled in the page. Naturally, you could also trivially hide the Taler option entirely by changing the visibility instead.
Note that you MUST select Taler here for the demo to continue, as the other payment options are just placeholders and not really working in the demonstration. Also, it is of course possible to ask the user to make this choice already on the previous page (with the shopping cart), we just separated the two steps to keep each step as simple as possible.