If the root canal had been filled farther than what we can see, and THEN the root resorbed, then some GP would be sticking through the apparent apex. It certainly looks resorbed and that your green line indicates the original apex, but I'm thinking that someone root-filled it AFTER the resorption and did the best they could. Whether this has worked to stop further resorption would require that the patient has no other signs or symptoms, and that we could get a radiographic timeline if possible.
So is this a patient that has come into your surgery for the first time? Do you know any details about the root filling, like when it was done?
Sure, you can PM me if you wish, but it's not a bad idea to put it up here for all to see - other dentists might have different opinions.