Twelve baskets for the remains of five loaves?
Sounds like multiplication to me.
It could have happened in more than one way: Jesus made 5 loves into 5,000 then they shared them, or he made the five loaves so bountiful that the pieces from them fed the multitudes with twelve baskets left over. You can use the word multiply to describe the latter explanation, but you don’t have to, as he accurately points out the word is not actually in the text.
Regardless, what he says in this sermon is 100% orthodox and in no way does he deny a miracle. Indeed he explicitly says that a miracle occurred. So the quote from Pius about naturalism is not on point.
There’s no lack of dubious sayings by Francis to criticize. This sermon is not one of them.
One more point. I just reread the quote from his sermon and he actually does say (contrary to the erroneous headline of this post) that there was a multiplication, but it’s not the emphasis of the story:
“In effect, the emphasis is not on the multiplication but the act of sharing.”
You may disagree about whether the emphasis is or should be on the multiplication, but regardless the headline quoting Francis as saying there was no multiplication is factually incorrect.