When the northern kingdom was exiled the Assyrians brought a mixed multitude of captives from kingdoms they had already conquered, and settled them in the largely now-vacant lands of the northern kingdom. By the time they were transplanted there by the Assyrians the north was already commonly referred to as "Samaria" (Samaria is the english equivilent) which had been Omri's capital. They adopted portions of the beliefs of the Israelites at least for the sake of "making peace" with the G-d of the land, and hoping to fend off the wild beasts of the land. Keep in mind this was hundreds of years after the exodus, and came after the settling of the land, the establishment of the kingdom, the split of the kingdom, and the fall of the northern kingdom.
Israeli tourist killed after falling off cliff in Jordan (Haaretz)
from the article: Ancient Samaritan sect marks Passover sacrifice near Nablus