I've been doing a bit of further online research. Nothing on the Southwark website about any changes there, and the map
they publish of the area still shows what looks like a right turn lane. Then I decided to check the TfL cameras that are at the junction with Humphrey St, (they show up on the map when you scroll down the list under map legend and enable them) and the one looking north-west up the Old Kent Rd clearly shows a right-turn lane in operation for turning into Dunton St.
QED, as my maths teacher used to say. The reporter was wrong.