The OP hasn't stated whether the resident in question already has an ONT installed in their unit or not, although it does specifically state a fibre cable is damaged rather than just a duct or conduit, so on that basis I assume an ONT is indeed installed but has a red optical signal light.

Assuming a pre-install has been done in full and an ONT exists that has just never been activated, then to me there seems to be two options:

 

1. You or the resident can use the Chorus network damage online form to report the damage, and give as much information as you can. This form has several additional questions that you may be able to answer, such as did you or someone else cause the damage? If someone else, were they a contractor working at the site? If so, do you know their business name and physical address? Information like this can lead to Chorus fixing the damage and billing the responsible party rather than the person who merely reports it.
2. The second option (assuming the resident is ready to connect to fibre) is for the resident to contact an RSP and place an activation order. Once activated, they can then immediately log a fault with the RSP, and a Chorus fault technician will be dispatched. Once again, the resident can explain that they did not cause the damage themselves, and that they believe a contractor is responsible. The fault tech will fill in a network damage report with all this information prior to fixing the damage. It is likely that the resident will then not be charged for the repair (but denying liability to the technician is crucial to ensure this). Even if the resident does receive a bill for repair from Chorus, they can still dispute the charge with the Chorus billing team and seek for it to be overturned by again stating that the resident did not cause the damage.

There's no need to overthink it. If your resident (or the resident association) didn't cause the damage then neither of you should have to pay for the repairs.