Pulford is saying that investigation into health matters of ancient historical figures is only justified if it is driven by a legitimate scientific inquiry rather than mere curiosity. Varela responds by saying that it is impossible to distinguish between the two because curiosity is at the root of any scientific inquiry. Varela thus contends that Puflord's whole argument depends on one being able to distinguish between a legitimate scientific inquiry and mere curiosity, but since curiosity drives both and curiosity often leads to scientific discoveries, this distinction is largely untenable.
Let me know if this makes sense and if you have any further questions.