It's one of the books in the Kobo store made available only in their kePub format with no alternate download options (most books have an alternate download, but it seems kePub only titles are increasing, or at least reports of them). It can only be downloaded with a Kobo device or app. What some do is use the Kobo desktop software to download and get the file where they can add it to Calibre and turn it into a "regular" ePub.
This article talks about how a person can tell ahead of time if a book will have an alternate download...
http://dearauthor.com/ebooks/making-...be-downloaded/