Adult Fiction Ebooks outsell hardcovers

Reuters had this piece.  But what does Reuters (the Brits) mean by "adult fiction"  Over here adult fiction means porn.  But it outsells hardcovers?  Do they have hardcover porn in the UK?  Or does Reuters mean fiction aimed at grownups as opposed to children and "young adults"?   And what about paperbacks?  Seldom do I pay hardback prices when I can wait a while and get it for paperback prices.  And even paperback prices are outrageous.