There were rules against using AI, they're just arguing that they weren't in the "Student Handbook".

If you click through to the legal filing linked in the article, they lay out that they informed the students of the rule during a lecture, they have a record of his attendance at that lecture, and parents also got handouts during a parent teacher day.

edit: quote

During the first week of class, RNH and his classmates were given a copy of HHS’ written policy on Academic Dishonesty and AI expectations.4 The students are clearly informed that this policy applies to all classes, not simply ELA classes. The policy was distributed in RNH’s class on the same day a PowerPoint presentation entitled “AI & Schoolwork” was presented to RNH’s class.5 This is the PowerPoint presentation referenced in paragraph 129 of the Verified Compliant.

Attendance records show that RNH attended the class at which the policy was distributed and the PowerPoint presentation was shown. Furthermore, the written policy was also posted on Google Classroom, on online portal containing policies which is accessible to HHS’ students. It was also distributed at Parent's Night which was held in September 2023. If RNH’s parents were present at Parent’s Night, a copy would have been provided to them.6