Hi Lennard,

There is no street-sign on site where it says this oneway highway isn't for cyclists. 
Check recent streetview imagery here:
https://www.mapillary.com/app/org/osmbelgium?lat=51.1638469&lng=4.9755271&z=17&pKey=1008447730183985&focus=photo&x=0.4082514773703663&y=0.5581186935100784&zoom=1.533219761499148