There is "cave diving" and "cave diving" and for the former, yes, pretty much a trust me dive, but for the latter, perhaps not-so-much.
My first "cave dive" was done in a single AL80 and led by an instructor who gave me a 15-20 minute orientation (perhaps a bit longer) on what I would see, etc. This was, of course, one of the vaunted Cenote Tours (and NWGD went with me on the second one I did). Was I "trained" as a cave diver at that point? No (although I, and Bob, certainly had more training and experience than the vast majority of people who do these tours). But even though we stayed within the Cavern Zone, we were, in fact, in a cave and we trusted our guides, AND OUR EQUIPMENT AND TRAINING, to get us safely through the experience. They were "Trust Me Dives" to some extent.
Since we have both continued on with Cave Diving, we have both gotten the instruction, prior to entering the "rest of the cave" and had much less "trust me" aspects to the training (and subsequent) dives. But, in fact, there IS an element of "trust me" in all training dives since we are being asked to do things we haven't done before.
For the diver discussed by the OP -- depending on what he does, I don't see a problem with someone doing a "cave dive" to see what it is like. I did (and made sure I stayed on the "right side" of the dreaded Cave Sign).