Let's use a plausible club diving situation:
I go diving with my club, and formally, the club is the official arranger of the outing. As always on club outings, the role of dive leader is on rotation, so everyone gets to go into the water. One of the dives is at a site I've dived several times, so I volunteer to sit out that dive and stay on deck as the dive leader. The job is basically providing a site briefing and counting heads to make sure that everyone who splashes has surfaced before we leave the site. The next dive is at another site, which I haven't dived before, so another clubmate takes the job on that dive. I have a CMAS*** cert, so I hold the qualification. My clubmate has a PADI Rescue cert, so she doesn't hold the qualification.
By your logic, I would have been on the hook if something happened on the dive I was overseeing, but my clubmate would have been off the hook if something happened on the dive she was overseeing. Is that a correct interpretation of the sentence I quoted?