iphone was linked to an unknown uid

Once I synced my iphone to itunes imessaged stopped working. So I went tnrough the process of resetting the phone. It is at this point I found out that the apple ID associated with the phone was an unknown one. I took the phone to the apple store ( I still had the receipt, it saved my ass) and they told me that it was changed a week prior. They where able to reset it. They told me that to change that you need physical access, know the the passsword for the phone and my appe id yo change it to theirs.

I find it hard to believe since if they knoew he passwords and had physical access theh would of just stolen the phone.