and 17 must stay

My opinion: most popular association. Most people were introduced to minesweeper through Windows. I don't think the author is necessarily name dropping, but just setting the stage in the most familiar way for most.

At least I hope rows are numbered top down like in "2D arrays", and not bottom up.

An array with an empty array is perfectly reasanoble to be able to represent the state of a matrix with rows and columns

yes, they both are

no because it's x and y like indexes of a 2D array, not x and y like in "real life axis"

edit: right, I'll update the description for consistency

edit²: done

A matrix is a rectangular array of numbers represented in this case with two arrays since ruby doesn't support the a "matrix" type natively

I removed the first statement as I see it could be confusing.

Matrix are conposed by two elements rows and columns

spoiler flag... x(

(and yes)