For me as a scientist "XY coordinates" most likely means cartesian coordinates. In SVG (like virtually any other graphics file format), coordinates are given in a cartesian coordinate system by default.
However, what is meant here is: "Turning an SVG into a dot matrix" or "Turning SVG paths into a series of dots".
The purpose of the author is mainly to emphasize clarity of animations.
Changing the size and color of the dots yields no new information about the operation of the algorithm. The dots are just a way to visualize the coordinates on a plane.
My point was the emphasis on "XY coordinates". It is just a suggestion to be more precise here.
The animations interpolate the dots between different XY coordinates.