FAA is deep into a power grab with respect to commercial use of drones especially small UAVs (sUAVs) that would typically be classified as RC in the past. They have a hard job to integrate them into the NAS but there is an immense amount of politicking going on around this issue right now with a lot of DoD contractor money in the drivers seat. Unless it's a formal notice (a phone call is not) he does not have to do anything. He should probably contact an attorney anyway though. A number of them are now specializing in this area.
If you are interested in this kind of stuff you should join this meetup my Co-Founder and I run: http://www.meetup.com/SF-Drones-Startup-Meetup - We just did "US Drone Regulations" last thursday.