Is this a true story? Yes!
Consider that in parables Jesus consistently used nameless characters, like Luke 19:12
He said therefore, A certain nobleman went into a far country to receive for himself a kingdom, and to return.
Or Mark 4:26
The kingdom of God is like a man who casts seed upon the soil
Another parable from Mark 12
A certain man planted a vineyard, and set an hedge about it...
Now, BAM! He mentions 2 persons Abraham and Lazarus, by name. He does not mention the name of the ruler because He has honor. This is a historical account of 2 deceased persons and their interactions with Abraham, who all still exist as I type this.
Also recall Mark 12:26-27
And as touching the dead, that they rise: have ye not read in the book of Moses, how in the bush God spake unto him, saying, I am the God of Abraham, and the God of Isaac, and the God of Jacob?
God of the dead, but the God of the living: ye therefore do greatly err.
It's not that complicated, if you ignore the sick and infirm person at your gate every single day as you live in luxury, you are wicked. You should have done something to help the person. He had his good things (which he should have shared) and Lazarus had his bad things (which he should have been assisted with).