John, in that instance was there a dive briefing in which the couple had the opportunity to participate? If so, was the dive profile explained? Was the fact that it was an overhead environment explained? Were any options given for these divers to remain outside the chimney? Did the couple object at all, express any worry, or even ask for a reassurance? (IOW, were they actually "told" or assured that the dive was within their capabilities by the DM?)
I don't know that this happens in Cozumel, but here it's possible for a hotel tour desk to simply book people onto a tour of any sort, and the girl doing the booking is generally not even a swimmer, let alone in any position to advise a diver of the appropriateness of a particular dive. "Oh a wreck dive? That sounds cool! Let's do it!" So we get brand-new divers booking onto dive trips to the
King Cruiser wreck, which sits at 30-32 meters in sand with ascent and descent on a current-swept line tied to the top at 17-18 meters. IMO these folks have no business doing this dive without some accommodation for their inexperience (I keep them only on the top of the wreck and don't do the sides or the swim throughs). But when booked on any tour, I do think it's important for all divers to recognize their responsibility to actually
participate in briefings, to ask questions, and to clarify the hazards of the dive so that they themselves are in a position to decide whether to do the dive as briefed or ask for accommodations.