I see several reasons for him to say it, yes. I dont see any reason for him to lie about it.
What would he have to gain? It wouldnt lead more people to his podcast, because most people will read it on a third party site (i.e., here) and not bother about the source. And if it even drove more people to DaringFireball, he wouldnt get more ad revenue, because The Deck doesnt deal in impressions he gets a fixed rate each month.
And if its not true, itll eventually come out (another company that was involved in the development may decide to leak some information, for example). In which case, Grubers reputation will receive a large knock (though Im sure hed find some way to spin it.)
The logical reason to break the story is because its interesting, and it leads to interesting questions such as will iOS devices eventually switch to USB Type-C?.