The car belongs to the individual named Koen Van Hove (as stated in the blog). He holds GDPR rights to any location data that gets sent out.
Before that, if the system allowed for any correlation of location data to who was driving at that point, the exact same rights apply too for each involved driver.
Only if the data controller (the entity who made the choice to put a gps tracker on the car) took specific steps to ensure the location data could not be correlated to an individual (and can prove those steps were taken), is the data safe from GDPR.