Depends i guess. We need to know a bit more about the incident too, why the passenger was disruptive, was alcohol involved, was this served by the airline, did the passenger show any signs before boarding (but was still allowed to board), etc.
The courts have held that knock on delays aren’t ‘extraordinary’ for the purposes of EU261, but the issue of a disruptive passenger, might be considered differently.
I guess on the basis of EU261, events such as these might be seen as part of running the business.