There kinda is though, this is true for almost all military gear: it's quite hard to hide the existance of a new tank once you're actually making it in large quantities, for example, but the detailed drawings of it, and the test results showing the strengths and weaknesses of it will be varying levels of secret. In the case of a listening system, it's the kind of thing which is pretty obvious to do, but the exact nature and means of it being secret makes sense (cageyness about the name of the system is odder: but it may be a concern about revealing exactly which system this came from, assuming there's multiple, for correlation with other information which may be less public).

(The same thing happened with the snowden leaks, BTW: it was suspected for a long time that the NSA or FBI had a survellance system similar to PRISM, because it's the kind of thing that they would want to do and have the means to do, even absent any concrete evidence of its existance. The leaks just confirmed the existance undeniably and also showed how extensive it was)