Yeah its not a number station at all.
Where the article loses me is the implication that this is somehow sinister or beyond the pale: it's just piggybacking on a global transmitter network that exists anyway, why not?
We don't know that it's a key that's being sent. For all we know, it could be just random data. Obviously it's most likely not random data, but ciphertext. Either way, we have no idea what the message is.
Well, you could look at it that way, or you could say that the fact that it's broadcasting all the time is the steganography. That constant transmission of nonsense that nobody wants is what makes it fail to be suspicious when you send a message that somebody does want.
Civilian high precision surveying has been reverse engineering raw GPS since the Navstar sats and swapping notes on back channels.