I'm not sure about that. In one sense, it's obviously yes.
But in a social setting where hijinks of this kind have long been acknowledged as harmless fun, and where the teacher has repeatedly gotten feedback that what they're doing is okay and even desirable, it's different.
The prevalent workplace norms have an effect on the people that work there. Stay in one workplace long enough, and you start to lose awareness of any outside context that might act as a counterbalance. What might seem weird or bizarre to an outsider ends up seeming pretty normal to long-time insiders. (This can actually be a problem for people like young college grads who are entering the workforce for the first time, and don't yet know what the norms are. If they land in a dysfunctional organization with their first job, it can poison their understanding of appropriate workplace behavior and cost them better jobs later on.)
So I'd give it a "qualified yes".
Yes, they probably should have stopped and asked themselves at several points along the way. But if they'd been getting enough positive feedback over a long enough period, the instinct to stop and ask may have been dulled to the point of uselessness. I don't think that they can be wholly to blame for such degradation of awareness.