Well it is more complicated than tat:
There are about 90% of French-speaker residents, and 10% Dutch.
Among these, a small part is actually not any of these two, but English or other non-official language, partially due to the large amount of people working for the EU.
In the day, you find a lot of people speaking Dutch because many living in the suburban area come working in Brussels (but also lot of French-speaking people live outside and come work in the city), hence traffic problems.

I do not find that driving in the city is especially difficult Parking either (when you know where to park, at least in evening - in the day indeed parking in the centre is too expensive).
Local do not drive fast: it is tourists who drive slowly!
Lasne is one of the most expensive areas of the country. I guess the guy has a big SUV; if he was driving a small city car he would have less problems in the small streets

But to go in the city centre in the day, it is indeed useless in car: too crowded, and the city is not that big. Most of the things to visit in the centre can be done by foot, and using the metro to reach what is a little further from the centre.