Buddha is referring to NEITHER pleasant nor unpleasant feeling, which results in the underlying tendency of ignorance or confusion to arise.
For example, we see a small green man walking upside-down on our ceiling. We look staring at it in befuddled amazement. We do not know what it is. It generates neither pleasant nor unpleasant feeling in our mind. Our mind neither runs towards it with greed nor runs away from it with aversion. The mind circles around the little green man wondering about it, with confusion and ignorance.
Or when Africans or Amazonians in the jungle first saw the white man, with metal armor, white skin and all sorts of trinckets and things they never saw before. They stood their in amazement and wonder until they received a gunshoot wound or saw a few of their own dead. Then they understood the signifance.
Our mind does not understand its origin, its cessation, its attractiveness, its danger and the way to escape the danger. Buddha taught like this about neither pleasant nor unpleasant feeling. (See MN 148 and the Pahana Sutta as examples).