The url of the project is in 404 but according to the date of the node creation i believe it's linked to this : https://www.rtbf.be/article/reouverture-des-commerces-un-site-web-pour-connaitre-en-temps-reel-l-affluence-a-la-rue-neuve-a-bruxelles-10646982

and from the same team a headmap visualisation (with osm map) : https://opera-wcg.polytech.ulb.be/en/projects/crowd-monitoring

Real data time was here : https://www.rueneuvebruxelles.be/ and is also in 404 for the data.

Unless somebody want to contact ulb the sensor (wifi) is probably gone (innoviris scale up found is generaly short term funding (up to max 4 years)  and since there is some improvement to have anonymised data for 4g/5g operator. (was in there planning when they begin the research : https://archive.ph/XyOiP ) it's probably useless.