Answer:
We have to go into Bible history to answer this.
Anciently, the tribes of Israel separated into two nations: the House (or kingdom) of Israel and the House (or kingdom) of Judah (the Jews).
The Jews maintained Jerusalem as the throne of their kings, while Israel's kings ruled from Samaria.
In the course of time, the continuous unrepentant sins of the House of Israel caused their removal from the land by God, who allowed the invading armies of Assyria to defeat them... and carry them away from their homes and land. They were scattered among the nations in the world and became known to history as "the lost ten tribes of the house of Israel."
"Therefore the Lord was very angry with Israel, and removed them out of His sight: there was none left but the tribe of Judah (the Jews) only... the Lord rejected all the seed of Israel, and afflicted them, and delivered them into the hand of spoilers, until He had cast them out of His sight...
"...So was Israel carried away out of their own land to Assyria unto this day. And the king of Assyria brought men from Babylon, and from Cuthah, and from Ava, and from Hamath, and from Sepharvaim, and placed them in the cities of Samaria instead of the children of Israel: and they possessed Samaria, and dwelt in the cities thereof..." (II Kings 17:18-24).
The Samaria of Jesus' day was of these roots... a pantheon of pagan Gentile religious beliefs tempered with a base understanding of Jewish laws.
"...they spake to the king of Assyria, saying, The nations which thou hast removed, and placed in the cities of Samaria, know not the manner of the God of the land: therefore He hath sent lions among them, and, behold, they slay them, because they know not the manner of the God of the land. Then the king of Assyria commanded, saying, Carry thither one of the priests whom ye brought from thence; and let them go and dwell there, and let them teach them the manner of the God of the land. Then one of the priests whom they carried away from Samaria... taught them how they should fear the Lord. Howbeit every nation made gods of their own, and put them in the houses of the high places which the Samaritans had made... the men of Babylon made Succothbenoth... the men of Cuth made Nergal... the men of Hamath made Ashima... the Avites made Nibhaz and Tartak... the Sepharvites burnt their children in fire to Adrammelech and Anammelech, the gods of Sepharvaim..." (verses 26-31).
In Jesus' parable, then... that would have been the Samaritan's religious background - utterly pagan.