A citizens' assembly allows you to choose members in a way that ensures that the demographic is representative. The demographic was equal parts men and women. They included representatives from all ridings in B.C., and they also included aboriginal representation. There was a much more diverse representation than there is at town hall meetings or things like that.
For a citizens' assembly held on a national level, you could decide what kind of demographic representation you want. There's no one set way to do that.