This publisher often lists the download versions first. Then the physical version show up listed later. It's happened before with titles from them I've eventually been able to purchase a paperback copy of. So I'm sure that this title, like all his other titles, will eventually be listed in a physical form. Most likely paperback.
The last example of this was this title of his from the same publisher.
https://www.bigskypublishing.com.au/...ret-submarine/
which was listed in a paperback about a month after the download was listed.