Well yeah, you're correct in one sense:
Ex post, we can say it wasn't a bluff. But -- and here's the critical component -- WMAL wouldn't have knownAs I have always understood the term, and as most dictionaries seem to define it, "calling a bluff" means to make somebody prove if he is serious about a threat -- WHETHER OR NOT the threat is real.
In other words, you "call the bluff" precisely to find out if the other side is bluffing or not.
Or, ex post doesn't equate to ex facto, as we used to say in my logic class. Or was it my Latin class? Can't really recall!
Well put. English is a fun language.