2.8g of total fat. Of that 0.4g is saturated fat, 0.9g is polyunsaturated fat and 1g is monounsaturated fat. Adding saturated / polyunsaturated / monounsaturated yields 2.3g of total fat - not 2.8g. What's composing the remaining 0.5g of fat?
There are different compounds included in the "total fat" calculation, which do not belong to any of the three classifications. Most probably, the larger part of the missing 0.5g are some kinds of phospholipids.