BRUSSELS — Belgian authorities tightened security Thursday in the port city of Antwerp after a Frenchman drove his car at high speed through a busy shopping area, forcing pedestrians to jump out of the way. French President Francois Hollande compared the incident to the attack in London that killed three people Wednesday, saying the Frenchman was “trying to kill people or create a dramatic event.” At first sight, the incident appeared to have the hallmarks of several extremist attacks in Europe — a vehicle in a busy area bent on mowing down pedestrians. The high-speed event happened a day after Belgium held anniversary remembrance services for the Brussels airport and subway attacks, which killed 32 people on March 22, 2016.