I'm guessing that a lot of people who took this quiz were from the Netherlands, looking specifically at which cities were guessed. The two most common (non-perfect) scores are 10 and 28.
Okay, the data for this quiz is really interesting to me. Only 164 people have taken this quiz since it was reset (so the sample size is slightly small), but there are several common scores. I'm guessing scores change depending on where people taking the quiz live and where they are from. Dutch cities are more likely to be guessed then Belgian cities, although I'm not sure how many people guessed them because they are Dutch, versus the people who guessed them because cities in the Netherlands are argueably more widely-known. Either way the stats get more interesting as time goes on!
Unforunetaly, the data isn't correct. For example, the municipality of Brussels only has 180k inhabitants. Maybe the agglomeration has been taken in some cities. in other cities the whole municipality isn't included, only the main city. (e.g. mun. Breda with 185k inhabitants.)
As I specified in the caveats the population is by urban area, not official city limits nor larger municipality. For example, my figures for Brussels includes surrounding cities that are next to Brussels (Brussels and Schaerbeek are seperated by a narrow road, so it makes sense to combine them into one for quizzes like this). On the other hand, data for municipalities includes rural expanses. Urban area figures remove the rural population in favour of people who actually live in the urban centre itself.