For those who don't understand the significance of this I highly encourage you to learn about ray tracing and the complexity of it. If combining something that complex with something so simple (Notepad.exe) is not art I don't know what is.
Ray tracing, at it's core, is actually beautifully simple.
Also, ray tracing is absolutely not the interesting (or "significant") part of this article. I highly encourage to RTFA first.
As for combining the two: having read on Raymond Chens blog about all the optimization that went into Notepad over the years, I'd guess Notepad is the real complex part here.
This example is a cube and plane with one light. It is lines from the camera checked for collision against triangles then a line from the collision point checked against a light. Checking for collision against a triangle is just checking collision against the infinite plane and checking if that point is inside the triangle.
What is the "significance" you are talking about? This is something common with an uncommon display.