Yes....The correct term is '66% Chance for Het' - meaning that there is a 66% chance that the wild type looking animals from this mating *may* be a het but because the 100% Hets and the wild types look the same, the only way to know one from the other is to breed them out.
You are correct. Because in theory 2 out of the 3 wild looking types are 100% hets. Making it a 66% chance that any individual wild looking type, from a het to het pairing, could be 100% het. eg 2/3rds.