The letter is the piece to move, and the number is the index to move to, starting from 1 on the left. The first alphanumeric pair is your move, then the computer's move. Comma. Your move, computer's move...

The first move after the comma is yours (open with kNight to 4), and the second move is apparently predetermined or always chosen.

the notation is just an array of move tuples, each tuple contains 1 move for white and 1 move for black, where each move is written as <1st letter of piece name><destination square>

There's a coordinate-based solution in the source code issues. I couldn't elucidate that notation either.

https://github.com/Rowan441/1d-chess/issues/1

Edit: There's a second solution where instead of moving the rook back 2, move the king forward one and the take the black knight with the rook as the checkmate move.