Your test section is supposed to be on the a section representative of the overall all condition of your paint. If the rear of the vehicle is much worse than the front, you should have done your test section there to get an accurate idea of what kind of labor you were looking at. The only reason that they always do videos and demonstrations on hoods is because it is much easier to see from a crowd and much easier to film, not because they necessarily recommend doing your test section there.
Also, the damage incurred did not come from any technique shown in their paint correction, but rather from contamination that was not removed from the vehicles surface before beginning paint correction. I have found the paint correction method to work just fine, though it will change slightly depending on your technique, the tools you are using, and the complexity and condition of the vehicle you are correcting.
I do not believe the videos are at all misleading as a whole, but were maybe misunderstood by you when viewing them.