Was the girl annoyed/upset or turned off by this? Was this a repeated offence (yes)?.
If both of those answer and yes, this was sexual harassment.
I'm not saying even if it was the kid should have been suspended, but some sort of action would have needed to be taken.
Maybe the school didn't want to suspend the kid, but took into account what appears to be multiple discipline issues, and found suspension to be the next logical step.