Some local municipalities may consider it trafficking child pornography, even if it’s a child doing the trafficking. That may explain the fine. I think there should be consequences for both parties. I don’t think you should just blame the boy for circulating a picture a girl made the choice to send him in the first place. Choices have consequences. For everyone.
I send several things per day. Everything that I send has a disclaimer. If a girl sends a picture to a guy she would be slightly more bright than dim to attach a disclaimer that says it is intended for the person it was sent and that the person receiving it is not allowed to duplicate, replicate, forward, or diseminate under penalty of law.