I suppose it was called this because it was supposed to stimulate gossip (tea contains caffeine, after all).
It appears as 'scandal-broth' in the preface by Sir Walter Scott to his Peveril of the Peak
There is a novel Scandal Broth by
(Fawcett, 1987; reissued, 1998). I haven't read it, but it sounds like a bodice buster.