This should be looked at as two clearances, the first was an enroute dir>cegan which requires an altitude at or above MEA/MCA. In this case MVA was used because they were off route and no MCA existed for the next segment being the IAP.
The second clearance was the for the VOR approach. The crew was responsible for this portion and the controller should be monitoring the progress and altitude, that didn't happen.
A terribly dangerous clearance that still baffles me, and then backed up with the statement, "I gave 7800' or above"? Did ATC really mean that? has he given this clearance before? will he do it again? not likely.
The crew lived to learn a valuable lesson the hard way and we have the comfort of debating their lesson on the keyboard with the hindsight being 20/20.
I'm sure that part of their acceptance of this clearance was the preconditioning from being assigned altitudes below published when being vectored to final. As we all now this happens on a regular basis.
No excuse, just trying to understand how one gets there.