I see, but then I still think there's something fundamentally wrong with the versioning of the developer edition.
I understand it's unmanaged and I also understand the difference between managed and unmanaged, but unmanaged doesn't necessarily mean unmaintained.
So if there is an update for the developer edition then it's still expected the app is automatically updated, because that's what Cloudron tends to do: keep apps updated to their latest (packaged) version.
And in fact Cloudron DOES update all packages automatically (unless you manually turn this feature off).
Moreover, according to the Cloudron store the package "org.wordpress.unmanaged.cloudronapp@2.14.4" contains Wordpress 5.9.2 whereas "org.wordpres.unmanaged.cloudronapp@2.14.5" contains Wordpress 5.9.3.

(this is a screenshot from the Cloudron store for the Wordpress Developer package org.wordpres.unmanaged.cloudronapp@2.14.5)
So if my Cloudron updated my Wordpress Developer package from org.wordpress.unmanaged.cloudronapp@2.14.4 to org.wordpress.unmanaged.cloudronapp@2.14.5, which it did, then Wordpress is in fact updated from v5.9.2 to v5.9.3 according to this information.
And the updates section in the Cloudron dashboard confirms this (cfr screenshot in my initial post).
So as a result of all this I still expect the version in the Wordpress admin area to be v5.9.3 and not v5.9
That the plugins aren't automatically updated is to be expected since it's the unmanaged version of the package, but not so for the core of the software.