An agency rule defining a certain class of model aircraft does not contradict the safe-harbor from an earlier law, as it imposes no more restrictions on the devices than does the earlier law.
Law did not implicitly incorporate an agency regulatory structure that exempted model aircraft; the provisions of the statute empowering the agency to regulate unmanned craft, read in conjunction with the definition of model aircraft within the safe-harbor provision, provides sufficient authority.
https://www.cadc.uscourts.gov/internet/opinions.nsf/E7D324AB37D6FC46852582C20052C10E/$file/16-1302.pdf
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.