Yeah but people who read this don't know that, and if it is 6 or 600 the word 'all' denotes a broad generalization.
But even if you weren't the topic in general is, it says 'Do girls like Negima?' Which implies that 'all girls may or may not like Negima' rather than 'some/most girls may or may not like Negima' just as 'Some/most guys may or may not like Negima' would be appropriate because not ALL guys or girls like/dislike Negima. So the topic itself is a generalization.
I payed way too much attention in Critical Thinking XD