"Daddy, tell the truth," Kathleen can say, "did you ever kill anybody?" And I can say, honestly, "Of course not."
Or I can say, honestly, "Yes." (Good Form.11-2)
Both truths work – O'Brien uses "honestly" twice to show us that. The "or," though, implies that it's a choice as to which truth to use. You can use one or the other, but not both, and O'Brien has clearly chosen story-truth over happening-truth.