Rob,
I know that sentence and its confusing as it has nothing to do with the absolute pressure accuracy .
Thx anyway 
From Bosch BMP180 Datasheet
Absolute accuracy
pressure
VDD = 3.3V
300 . . . 1100 hPa 0 . . . +65 °C Min -4.0 Typ -1.0* Max +2.0 hPa
Thomas