They were well beyond the sign. Click over to 23:24 in the videoYou should be able to see daylight from Devil's Ear right where that sign is located. It's right at the end of the cavern zone.
It's right after cave diver harry talks about the requirements for entry beyond the sign. In fairness, I guess he never says proper equipment is required - just that they be accompanied by an instructor as a guide. Which they do appear to be. I'm just surprised that proper gear isn't also a requirement.