For bodybuilding purposes, the shoulders are just those two rounded points at the top left corner and top right corner, connecting the arms to the trunk. Everything else on the trunk, from the neck to the waist, is the "back."
Some people train traps (the big chunk of meat running from the neck to mid-back) on shoulder day, but I disagree with it.
That's normal (though not necessarily a "good" thing"), depending on the exercises you're doing and your technique while doing them.
Check which exercises are listed by the majority of members, and choose those to target your intended bodyparts.
Out of curiosity, what does your shoulder workout and back workout look like right now?