In this case, "cheating" is defined as designing only to pass whatever the NHTSA happens to be testing now, and ignoring all other areas where things could go wrong.
edit: I'm not saying I agree with GP, just explaining what I think they meant by stating that they were "cheating."
That doesn't really seem to be the case, though. The NHTSA looks at highway and road data to determine what types of crashes result in the highest number of fatalities and then creates tests around those. If "cheating" implies that they're only designed to pass what the NHTSA happens to be testing then, by extension, the vehicle would protect the occupants against the types of crashes that are most likely to result in a fatality. That seems like huge win to me.
edit: I'm not saying I agree with GP, just explaining what I think they meant by stating that they were "cheating."