Well we don't know whether the patient with 'zero tumour burden'...

Well we don't know whether the patient with 'zero tumour burden' is that yellow line on the graph. I stated that the person is likely the one who achieved a CR. This graph just tells us about antibodies and we know there are only 7 lines. We know that 3 people are still living and are on the trial, however only 1 of the lines runs all the way to the end at 42 weeks. Given that the graph is aiming to demonstrate that a there is a correlation between dosage and antibody production between each of the arms, I think it does a good job at depicting that.
Remember our objectives in a phase 1 trial.

You're missing that every patient in the trial was in 1 of the monotherapy treatment arms, all with varying levels of IMU-201 (PD1-Vaxx), with no other treatment. So the only conclusion would be that the patient on the trial has had a health benefit from PD1-Vaxx and their immune system has been able to kill off the tumour with no reoccurrence 18months later.

Remember to be eligible for the trial, all patients needed to:
1. Histologically confirmed non-small-cell lung cancer (NSCLC) tumor stage IIIb or IV (3 major types of NSCLC are acceptable including squamous, adenocarcinoma, and large cell carcinoma);
2. Progressed on an approved PD-1 inhibitor or an approved PD-L1 inhibitor. Patients previously treated with a combination of an approved PD-1 or an approved anti-PD-L1 inhibitor and chemotherapy may be included with agreement of Imugene Limited

Sourced from A Study of IMU-201 (PD1-Vaxx), a B-Cell Immunotherapy, in Adults With Non-Small Cell Lung Cancer - Full Text View - ClinicalTrials.gov