Rule? It sounds like a law to me:
"15. Can I operate a jammer in the U.S.? No. It is a violation of federal law to operate jammers in the United States, except for authorized, official use by the U.S. government."
"15. Can I operate a jammer in the U.S.? No. It is a violation of federal law to operate jammers in the United States, except for authorized, official use by the U.S. government."
One way to get bitten by this is by working for the government. You might think you have a contract, and that for instance your pension is set in stone by the paper you signed. That would be a wrong impression, as that paper you signed is (usually) not in fact a contract, merely an acknowledgement of the regulation (the text will, of course, state that this is so), and that regulation, unlike contracts, can be changed without your approval.
It seems to me that the GP is attempting to technically point out that the most narrow definition of law only applies to what both houses decide and the president signs. That's not true in any meaningful sense.