Not a rule. They used the word "should" rather than "shall" and it isn't part of the safety code or an official policy. Worse is that it misunderstands the RFI problem.
RFI could result in your being unable to communicate with a wireless switch but it can't cause it to do things. At least if the communications are properly encrypted. If they really do have a problem with wireless switches then they also have a problem with wireless launch systems.
Magnetic switches require field strengths unlikely to be produced by anything other than powerful magnets. Items which are in short supply on the field.
Since relays have been mentioned I thought someone might be interested in a high dollar MIL-SPEC relay (rated for high vibration and shock environments) at
BGMicro. $1.50 each today which is way less than the original price.