Net impact carbs are a relatively new thing the companies have come up with since folks have caught on to glycemic index, etc. Net impact carbs are ones that have an impact on blood sugars, thus insulin response.
The remainder of the carbs like sugar alchols they claim do not impact blood sugars. I take all this with a grain of salt, for some sugar alcohols, though originally developed for diabetics do have a small impact on blood sugars. I had a chart at one time, will see if I can find it.
Anyway, the best thing to do in my opinion is ditch the bar, most of them are pretty much trash anyway. I eat them as emergency food only, a stopgap if you will if I need something quick. I always avoid them on a regular basis of any kind.