RE: Since he does not speak English, I’m not sure how he could be swearing in English.
It was an Italian equivalent of the English F-bomb translated into English.
If His Holiness was speaking his native Spanish, I could understand. While speaking a second language with two words that are so very close in their pronunciation, the brief stumble is easy to understand. Of course, papal infallibility does not mean that popes don’t make mistakes or stumbles.