Okay, so the clutter thing? Was pretty lame.

In fact, their result is totally expected. Because of the time reversal invariance of (most) physical systems, the only thing that would be unexpected would be not observing their result.

If, however, they had many dissipative objects in their field of view, implying what is called dispersion (and vice-versa), or many objects with other sources of current, then you might be surprised that their trick worked.

Even if you had external current sources, because there aren't that many sources of current with significant gigahertz components in their spectra, we'd kinda expect little in the way of unexpected differences.

That's not to say we'd expect perfec agreement, but, as in the acoustical case, I'd expect pretty good agreement. After all, real things are complicated :)