As strange as it sounds, sometimes people are able to access other's pages from clicking through other peoples profiles. Even if your is set to private. Trust me, it's happened to me. (I know every single person on my friends list personally, and I've had random people that MY friends are friends with click through and view it! I'm really private about my profile, and only want my REAL friends to see it. ) It is a VERY REAL problem, and you don't truly have "privacy" when" it comes to such media. Sorry.:(
It may seem really intrusive to you, but as far as privacy goes, anything online can easily be viewed by another person, whether it is a friend of your or a potential boss or University. It is very common, and not unlike a personal background or credit check. It isn't unethical or even illegal, although it really feels invasive. It's just browsing, after all, right? If you have pictures or things that would be embarrassing to you, it might be a good idea to remove them! If you look at it from the perspective that someone you don't know WILL see something you want kept private, and then tailor your page to suit that, you should be fine. I know, it sucks, but with so much of or personal info easily hacked or available these days, we kinda have to!
PS: If you are on their network, then YES, they can see much of what you are doing online! :(