"Furthermore, is that a checkmate at all? I'm not playing too much chess, but could someone point out, if this is a true checkmate?"
When that episode aired, I used a variety of chess pieces to simulate the chess position I saw in the screen-shoot. But my conclusion is that no matter which piece is the King, and no matter what the other pieces are, there is NO checkmate in that screen-shoot.
A pity, really. The "Noir" anime got their chess games done right, but not many other shows ever did that.