I assume you know this, but depending on what the enclosure was made of, what frequencies the devices inside were broadcasting at, and where you placed them inside, you could very well have accidentally produced a resonating chamber, parabolic antenna emitter, or other type of structural frequency-specific gain-boosting mechanism.

They likely wanted to just make sure that you hadn't done that. (And to do that, they had to send some fellows whose time was very expensive, because it takes long experience to build up an intuition for these things to the point that you're confident enough in your answer to not have to bother with the "measure everything and plug-and-chug the dynamics in a simulator" step.)