Very intriguing indeed.

It looks like an M2 sign here below the arrow, as if cyclists were allowed to ride contraflow on half of the part.
https://www.mapillary.com/app/?pKey=1921972068627879

For anyone making a survey: if the two access roads are still barred like here (https://www.mapillary.com/app/?pKey=1829466440969417), we should check how cars are supposed to enter Chaussée de Boitsfort/Bosvoordsesteenweg.  Perhaps along the tram tracks but from what I see in the same Mapillary sequence, it was not allowed…