The very much quoted 'Love thy neighbour' was first intended only towards jews. (I read it in God delusion). However, as the years passed, people's understanding evolved, the same judaism gave gems like.
I can see how the passage might be read like that. This was the original passage:
Lev 19:17-18
You shall not hate your fellow countryman in your heart; you may surely reprove your neighbor , but shall not incur sin because of him. 18' You shall not take vengeance, nor bear any grudge against the sons of your people, but you shall love your neighbor as yourself; I am the LORD.
NASU
However, with the rest of the text of the law, it is clear that the Israelites were to apply the same laws to all who lived there - whether Israelites or foreignors:
Num 9:14
If an alien sojourns among you and observes the Passover to the LORD, according to the statute of the Passover and according to its ordinance, so he shall do; you shall have one statute, both for the alien and for the native of the land.'"
NASU
And they are still commanded to love the aliens who were living among them:
Deut 10:17-20
For the LORD your God is the God of gods and the Lord of lords, the great, the mighty, and the awesome God who does not show partiality nor take a bribe. 18 "He executes justice for the orphan and the widow, and shows His love for the alien by giving him food and clothing. 19 " So show your love for the alien , for you were aliens in the land of Egypt.
NASU
So I think Jesus application of 'neighbor' to the Samaritans (seen as non-Jews at the time) fits with the overall tenor of the law with regard to individual morality and it doesn't seem to have been a gradual evolution as much as a radical challenge to how the religious leaders of the day had been interpreting it.