I've often seen CD's marketed as a soundtrack for a movie. Case in point:
This cd is listed as a soundtrack
http://www.amazon.com/exec/obidos/tg/detail/-/B00005K9KF/ref=pd_bbs_null_3/104-8262482-2240755?v=glance&s=music
even thought the only song on it from the movie is song that plays durring the credits.
The soundtrack is really this cd
http://www.amazon.com/exec/obidos/tg/detail/-/B00005LNIY/ref=pd_sim_music_1/104-8262482-2240755?v=glance&s=music
Your local music store probably only had the first one in stock.
Another such case is the first Michael Keeton "Batman". There was the actual soundtrack (with music by Danny Elfman), then there was the Prince "Soundtrack". Many people got taken by that one - I mail-ordered that one when it came out - oops.
At least the Narnia disc in question actually labels itself as "songs inspired by".