Why did God only cure Naaman? Jesus said (Luke 4:27):


  "There were also many lepers in Israel in the time of the prophet Elisha, and none of them was cleansed except Naaman the Syrian."


Several possible interpretations occur to me:


Others were cured too; Jesus is simply wrong or misquoted.
Others were not cured. (Why?)
Even Naaman was not cured, because miracles are fantasy.


What does the evidence say? Is there any extra-biblical source confirming Naaman's curing? Is there any explanation why the other lepers are not cured?

I am mainly looking for extra biblical evidence that would convince the agnosis. After all, if Jesus says so and it were true is not an assumption we all share. Moreover, Jesus often says vague things, (like the time is near) and easily misinterpreted things, like mustard seed is the smallest.
There are many accounts of people being healed in the Scriptures.  It seems that God sometimes used this to authenticate His message or His messenger.  Other times, it seems to be just an act of compassion.  The resurrection of Jesus is the most significant miracle, of course, and it is certainly not fantasy.  There is ample evidence to support the occurrence of miracles.
The particular instance in Luke 4 comes as Jesus is speaking in His hometown of Nazareth.  The people there are rejecting Him because they are familiar with Him and His family.
Jesus cites two examples where non-Jewish people were healed and Jewish people were not.  The Jews were God's chosen people, to be sure, but their history is one of consistent rejection of God.
This appears to be a warning to the people of Nazareth to not reject Jesus just because of their familiarity with Him.  In times past, God had turned from the Jews and bestowed His blessings on Gentiles, so just because the people of Nazareth were Jewish did not preclude them from being rejected by God if they rejected Jesus as the Son of God.

22 And all spoke well of him and marveled at the
gracious words that were coming from his mouth. And they said, “Is not
this Joseph's son?” 23 And he said to them, “Doubtless you will quote
to me this proverb, ‘Physician, heal yourself.’ What we have heard you
did at Capernaum, do here in your hometown as well.”
24 And he said,
“Truly, I say to you, no prophet is acceptable in his hometown. 25 But
in truth, I tell you, there were many widows in Israel in the days of
Elijah, when the heavens were shut up three years and six months, and
a great famine came over all the land, 26 and Elijah was sent to none
of them but only to Zarephath, in the land of Sidon, to a woman who
was a widow. 27 And there were many lepers in Israel in the time of
the prophet Elisha, and none of them was cleansed, but only Naaman the
Syrian.” 28 When they heard these things, all in the synagogue were
filled with wrath.
29 And they rose up and drove him out of the town
and brought him to the brow of the hill on which their town was built,
so that they could throw him down the cliff. 30 But passing through
their midst, he went away.  Luke 4:22-30 ESV