Indexing into 2D containers is often an exception to the "x, then y" rule; indexes are very often specified with "row, then column"[1]. It's true that this is different to Cartesian coordinates, but grid cells aren't points or locations on a Cartesian plane, they're members of a 2D container: the grid.

1: https://en.wikipedia.org/wiki/Index_notation#Two-dimensional...