The criteria for Papal Infallibility.
1. “the Roman Pontiff”
2. “speaks ex cathedra” (“that is, when in the discharge of his office as shepherd and teacher of all Christians, and by virtue of his supreme apostolic authority….”)
3. “he defines”
4. “that a doctrine concerning faith or morals”
5. “must be held by the whole Church”
So without the actual Papal Bulls of Clement we cannot determine whether his words were infallible. Although docuмents, such as bulls, are indeed fallible.