The training exercise was probably to give training for this patient transfer for both military and hospital personnel.
That makes sense.
Tim, perhaps you might have some insight into this: who is responsible for ensuring the landing site is suitable for the aircraft landing there? I mean, say the ATC at your local airfield gave you permission to land your 747 there, whose fault would it be when it all went horribly wrong?
I can't speak for the Americans - and it's a long time since I was involved in off-field operations - but for temporary or rarely-used strips as we used in the C130, there would be a visit sometime prior to the exercise to ensure that the site could take the load and that there were no avoidable intrinsic hazards (such as loosely-fixed surface coverings!). Any issues would be flagged up and would be checked as resolved a couple of days before the exercise. On the day, a Landing Zone Safety Officer would be positioned by road (or on foot if necessary) to make sure everything stayed safe throughout the process, and they would be in radio contact with the aircraft, either by discrete radio or by the airfield's own system if one existed.
Even back then, helicopter operations off-field weren't allowed without similar precautions except, of course, in an emergency (which could be a casualty pick up). I find it surprising that there wasn't a similar setup in this case. My RAF Helicopter Landing Sites (UK) book says that the helipad is owned by Downing College, not the hospital, and that planned casevacs should go via Cambridge Airport. However, that book is the 1982 issue so it's unlikely to be the same now, and Cambridge Airport is about to close - which may be why the exercise was run.
