Outline of theatre is a little bit suspicious and address of the building is certainly not 2F;4 Rue Hubert Stiernet - Hubert Stiernetstraat. 

https://monument.heritage.brussels/fr/buildings/36544

Official address of this puppet theatre is 460A : https://kbopub.economie.fgov.be/kbopub/toonondernemingps.html?ondernemingsnummer=418837090

Social media picture suggest that it's not so big but just a part of the building (otherwise why don't use monumental entrance ? ) 

Also on the building there is a ktichen maker valcucinebruxelles.be : https://www.mapillary.com/app/?pKey=464162221712149 

https://monument.heritage.brussels/medias/buildings/10208169/10208169_0458_P23.jpg

https://valcucinebruxelles.be/wp-content/uploads/2018/05/Cuisine-showroom-Valcucine-Bruxelles-2017-9.jpg

Posbox on 258 suggest there's other occupant too.