"In an informal context, the pope wanted to say that he always considers criticisms an honor, particularly when it comes from important thinkers, in this case, from an important nation," Bruni said.
The book purports to describe concerted efforts by conservative Americans to undermine and ultimately replace Francis as pope. It is only available in French.
During the in-flight press conference, Pope Francis said he is not afraid of possible schism, because there have been schisms throughout Church history, but he is praying it will not happen.
Describing schism as "an ideology separated from doctrine," he said it is "not Christian."
"It is one of the actions that the Lord always leaves to human freedom," he stated.
He also said he believes, however, that the People of God will speak up and help in such circumstances, "that there will be a correction if there is some mistake."
"Today we have many, many schools of rigidity inside the Church, that are not schism, but they are Christian pseudo-schismatic paths that in the end finish badly," he said.
"When you see rigid Christians, bishops, priests, behind them there are problems, there is not the holiness of the Gospel, for this we should be meek, not be severe, with the people that are tempted by these attacks, because they are passing through a problem, and we should accompany them with meekness."