I guess the Belgian cartoonist didn't speak Finnish and also didn't know that Musti is a traditional dog name in Finland. If you name your cat Musti in Finland, people will be very confused because everyone knows it's the most typical dog name there is.
Traditionally used especially as a black dog's name, as "Musti' is like a cutesy version of 'musta' (the color black). But it's usage is not limited to black dogs. Would be weird to come across, say, a white dog called Musti though. :D