The answer to this depends on which Item Ratings system you're using, so first check your template settings to see if you're on "Classic" or "Custom" ratings:
Classic Ratings
If you're using Classic Ratings, an item is marked complete if it has been 'touched' (i.e. you tapped into the item to view the comments within it or changed the rating) AND:
It is marked "NI" or "NP"
-OR-
All non-checkbox (i.e. Multiple Choice, Text, Number, Date, etc.) informational comments within the item have been answered
Keep this in mind when building your template and choosing the answer types!
Custom Ratings
If you're using Custom Ratings, an item is marked complete if:
It has been 'touched' (i.e. you tapped into the item to view the comments within it or changed the rating)
- AND -
All non-checkbox (i.e. Multiple Choice, Text, Number, Date, etc.) informational comments within the item have been answered
This means that Item Ratings don't matter in the Custom Ratings system! So your informational comments should either be deleted or have an "N/A" option for when they do not apply.