I don't think there is a good or straight forward answer to this question so here is my round about way of answering:
This may be due to the fact that you haven't always been private. I'm sure that this will update soon to not have your friends listed in it.
I tried this on a few private accounts (@brandi is a good example). She follows 15 people, which I can't see. So I clicked on her Similar to @brandi link and went through the list.
None of those featured showed her as a follower.
Also, your twitter account isn't private.
I compared the lists of "Similar to you" and to your followers and your following lists. 2/3 following were listed in your similar to, but both of those are public accounts.
Twitter bases those lists on the relationships between following and maybe geography. I'm sure there is some tweet context in there as well, but anyone seeing the similar to lists wouldn't be able to pin down exactly who is following you and who you are following just by those lists alone.
The way to get around social engineering is to leave Twitter. Really, the only way to get around social engineering is to live in a shack in the woods without electricity or human contact, but you're just trying to get around the lazy social engineers.