Yes you're absolutely right. I work in NVH dept at one of the car companies. We measure interior noise using mics which are accurate starting from below 20 Hz to 20 kHz. So this should be very trivial.
One of the frustrating things about "the hum" that the article mentions is that, academically, it's been lumped into the lunatic fringe of conspiracy theories, and serious scientists aren't interested. It does seem like the right equipment and expertise should pretty easily be able to determine, conclusively, whether or not any given "hum" is a real physical sound.
In one of my old apartments, I was able to hear modulating pure tone low frequency noise on some nights. I definitely could tell the noise was perceptible only during night. I think there could be many reasons for this noise from water filtration plants, power plants, to any other large industrial applications.