From discussions with Chief Ron Glidden some years ago, the answer seems to be NO!
Those involved in prosecuting such things opined that if there is ANY possible access to a room thru a window or unsecured door (see above case for opinion on what isn't a secured door) that it would be treated the same as a "locked house" . . . not within the law.
BUT, if you have a locked closet (with no other means of access) with a tumbler lock (or padlock), you have now created a properly locked storage "container".
IANAL, but if the cellar window had bars on it 3" apart, you might get a pass, but if it is a standard cellar window, a push breaks the glass, reach in and unlock the window and if you know how, most are totally removable so you can shimmy into the basement. Not secure at all and a real weak spot in many homes.