It doesn't make any sense if this digest was triggered by the new discussion or comment from the request, but if it was deferred from a prior action, I can see this occurring when a new feed or a new synonym triggers a digest, since neither feeds nor synonyms are "children" of pages, and would not have the 'pageid' index. For these types of content, 'areaid' should be used instead.
Additionally, it was possible for a user to receive a digest about a new feed or new synonym that the same user created.
Both are fixed in the next release.