Did you read that page, or did you just skim it? They're telling you to use a "headless browser" as one possible (clunky) way of responding to _escaped_fragment_ requests, which is a workaround wherein you put a special tag in your original page to tell the googlebot to make another request to get a static version of the page.

Using _escaped_fragment_ is not the same thing as rendering different content based on user agent.