How did this person I know find me on Twitter?

[Jordan]

I am very confused. This girl that went to my primary school has somehow found and followed me on Twitter. I don't use my real name and my username is not even close to my real name.
I don't follow anyone I personally know.
Has she somehow got my Twitter account through Facebook or hotmail.com?

I know it's her because in her profile pic on Twitter she uses the same Justin Bieber phone cover as she does in her Facebook profile picture.

Also, I noticed a few people I personally know on Twitter even though they don't know me.

[john]

prolly random or type in your name

[isayhello]

Twitter suggests people to follow. So maybe, you or her follow the same person and Twitter suggested her to follow you.