yes, canonical owned snaps like the snap-store one have been the exception to this policy (though indeed it could have been changed recently)
i also remember that we in general used to not allow managers for other package formats into the store, not sure if that rule still stands … IIRC @niemeyer and/or @jdstrand established that rule a while back…
EDIT: i dug up an older reply about the package management topic:
