The parent is not Informative, rev in this case is correct since the resource linked is a NOT the canonical page but a short-url version of the canonical page you are currently on, so the relationship is:
page A with long URL <--is the canonical url of--- page B with short URL
page A with long URL ---is another address for the canonical url--> page B with short URL
Page A is the canonical, the long URL page is the authoritative destination, page B is just a shortcut, and not the other way around, so when in page A, if your software are looking for alternate address of that canonical page with shorter urls your software should look for reverse links containing "canonical" as the value. Links for pages that have the current page as the canonical are the ones with rev, not rel.
See http://www.w3.org/TR/html401/struct/links.html#h-12.3.1 to understand.
I admit it is a little confusing, maybe they should be using rel="alternate mirror", rel="alternate short-url" or simply rel="alternate" instead, to indicate that the link points to an alternate version of the current page. But saying that the link is of a page that points reversely to the current page that is the canonical is not wrong