When C.D. moves a piece (his rook) and says 'check', it was not check. Hi rook was on the wrong row to put Trivette's king in check.
During an opening scene as Walker and C.D. are playing chess, C.D. places Walker's king in check and then Walker moves and announces checkmate winning the game. However, when a player's king is placed in check, that player must execute a move to release the king from check; either by moving the king to a safe square or blocking the check with another piece. Walker's move was therefore illegal according to the rules of chess.