Second, check your catechism. Ex Cathedra isn't enough. In this case, even if he were speaking Ex Cathedra it wouldn't be a sufficient guarantee. Infallibility is only claimed when he speaks Ex Cathedra on a matter of doctrine or morals applying to the whole Church.
Statements about Islam could never be considered infallible under the doctrine.
From Wikipedia:
Ex cathedra: In connection with papal infallibility, the Latin phrase ex cathedra (literally, “from the chair”) has been defined as meaning “when, in the exercise of his office as shepherd and teacher of all Christians, in virtue of his supreme apostolic authority, (the Bishop of Rome) defines a doctrine concerning faith or morals to be held by the whole Church.
Speaking on matters of doctrine or morals applying to the Church is IMPLIED in the term.
RE: First, you meant to say fallible.
I meant to say NOT infallible, but your statement is just as correct.