In the first paragraph it says:
You can also turn off anonymous comments and ban particular LiveJournal users from commenting in your journal, without affecting other users' ability to comment.
And then the final paragraph says:
You can, however, ban an individual user from commenting in your journal.
I also think it's quite easy to miss these suggestions in the FAQ. Maybe, for clarity, it would be better to have one section with "why it's not possible to ban a user from reading your journal" and another one listing "things you can do instead"?