You need to read the nature of the exception more carefully, as it does not require that the circumstances indicate that there is recording going on unless someone objects. It only requires that the conversation be taking place in public, in person, where the speakers have no reasonable expectation of privacy.
If your common sense tells you that two strangers talking at a public dive site, one of whom is wearing a camera in plain view on his head, falls within the category of in-person conversations that are private... then I'm quite sure I cannot help you.
Maybe the buddy was distraught? Diving is gear intensive, we do wear stuff on our head, and if the buddy was worried about the deceased diver it is possible that they didn't notice the camera.