It's not a completely random guess. Context informs the guess. For example, all the examples they give, and the books I saw when I scrolled through the underlying list their article is based on, seem to be about and banned for having gay sex, sexual abuse of children, sex with children, and racism. If they were equally interested in all banned books I think it would be an odd coincidence for all of their examples to be in that narrow range of topics. There are no books about how to run drug labs, commit genocide, or burn heretics among their examples? Odd...
It's not a completely random guess. Context informs the guess. For example, all the examples they give, and the books I saw when I scrolled through the underlying list their article is based on, seem to be about and banned for having gay sex, sexual abuse of children, sex with children, and racism. If they were equally interested in all banned books I think it would be an odd coincidence for all of their examples to be in that narrow range of topics. There are no books about how to run drug labs, commit genocide, or burn heretics among their examples? Odd...