I believe the technology used to detect the signals as described in the article was also used during World War II to detect radio transmitters of spies and other operatives.
Itβs very real technology.
Rather trivially, as any superheterodyne receiver from has an intermediate frequency oscillator that is mixed with the signal - and it is hard to not emit RF from that.
Modern equipment just tends to be better designed to tighter tolerances as both the standards on inadvertent emissions and manufacturing have been tightened so it emits much less - but still not zero.
