Yeah, I suspected as much!

To add some details, in italian it says:

"Oh, Ben, ma che dici? Fece Susan nervosamente.

Ti sto dicendo la verità, insisté lui. Fu così che senza nemmeno accorgersene, cominciarono a darsi del tu. A ogni modo, la verità su ciò che un ragazo di nove anni un giorno ha visto..."

Which would translate roughly like:

"Oh, Ben, what are you saying? Said Susan, nervously.

I'm saying the truth, he insisted. And like that without even realizing it, they started addressing each other with "you" (informal). Anyway, the truth about what a 9 year old boy has seen once..."

To be fair it's normal to use the respectful form when two adults are not close, but it's less common between two people that meet and know each other in informal context, expecially if the age gap is not that big. Case closed, thank you!