I could be wrong but if you unlock the screen and it isn't at the home screen, try hitting the back arrow until it goes all the way back to the home screen and see what happens when you unlock it again. This happened to me once when I tried to start a text and it took me to my picture gallery. All I did was keep hitting the back arrow to home screen and it fixed it.
EDIT: Please know that I'm not smart at this stuff yet but this is what worked for me.