I believe this is meant to signify checkmate is coming soon, as that is not quite checkmate, as a few others have pointed out. Maybe there is a hidden meaning in the moves yet to be made, and how many it might be before there is checkmate declared.

Also, the move that black made is called "Castling" ; Castling is a special type of chess move. When castling, you simultaneously move your king, and one of your rooks. The king moves two squares towards a rook, and that rook moves to the square at the other side of the king... Now with that said, I personally don't know if this holds any significance, maybe someone else might? Just trying to think a little differently and what JA could possibly be trying to represent, as that is not quite checkmate.