If someone whose audience is set to "public" posts on my wall, or comments on my status, is the public then able to see things on my wall even though my audience is set to "friends"?

In other words, if I post (which I wouldn't) "Leaving for vacation tomorrow" and "Susie", my FB friend whose audience is set to public, comments "Have a great time!", can the public (or Susie's friends who aren't MY friends) see my post and know that I'm going on vacation?

On that ticker thing, if I hover the cursor over a friend's comment, I can see status updates, photos, etc. on the walls of people who are NOT on my friend list. Is that because their audience is set to "public", or are posts that people think are limited to their friends being tickered to friends of friends, etc.?