It depends.

From: https://openbaarvervoerbelgie.be/over-ons/

* For companies publishing real time positions (STIB-MIVB, TEC), live position will be shown. For companies that don't (De Lijn, NMBS/SNBC), we calculate the position based on the schedule (GTFS), corrected with published delays (GTFS-RT).

Every vehicle on the map is labeled with realtime / calculated position.