Well, i don't know if this technique has a name, but i if i am correct:

what he is doing there is represent a set of colors as a sprite, for example the black color (0x000000) is represented as an empty tile and the white color (0xFFFFFF) is represented as a the "star" tile.

you just have to understand how RGBA works

You would need to load your image into a surface, then read it pixel by pixel determining the color value.
then map those color values to tile values.

Also note, if you have fewer than 255 tiles you can use the three other values as other data. There are a lot of neat things you can do if you choose to represent RGBA as something other than colors.

Eg: R can represent a tile while G represents the height and A is the id for a creature when it's non-zero. When I first understood this concept, I had a lot of fun altering game maps using Photoshop's filters and other image editing tools.

As an extra bonus, you can easily write shaders to manipulate and create maps. This is useful for quickly executing map generation algorithms.