Actually that is not true. As desert nomads they were a tribe of warriors. The Egyptians retained them as mercenaries to guard their border with Nubia. There is NO evidence they were ever slaves in Egypt.There is NO evidence that the Hebrews were ever in Egypt.
My personal opinion is that they resided in Egypt as mercenaries and learned much from the civilized Egyptians. Many Jewish practices were already present in Egypt, for example circumcision. Some time later they left Egypt and conquered and displaced the Canaanites who were their kin.