I wonder if he has someone in particular in mind.
Rorate Caeli reports:
A Pope has never been publicly questioned for clarification on a most sensitive matter (his own reaching office) of a more sensitive content (his own major document) by his own Cardinals at any moment since the Counter-Reformation. It is astounding: certainly unheard-of in modern times.
The letter containing 5 clarification questions (“dubia”) was signed by four Cardinals on September 18 — Italian Carlo Caffarra, emeritus of Bologna, American Raymond Burke, emeritus of St Louis and former president of the tribunal of the Apostolic Signatura, and Germans Walter Brandmüller, eminent historian and emeritus of the Pontifical Committee for Historical Sciences, and Joachim Meisner, emeritus of Cologne. They were sent with an accompanying letter.
Hat-tip, Vox Cantoris