Continuity mistake: When Josh is playing against his father for the first time, he is able to shout moves to him from another room (i.e. from the tub in the bathroom) to checkmate him. Later when he is learning from his teacher Bruce, Josh claims he can't solve a puzzle without moving the pieces physically.
Continuity mistake: When Josh and his father play a game of chess Josh's father picks up a piece from the centre of the board and moves it diagonally towards one of the flanks. In the next shot it is visible that the piece is a white rook, which can't move that way. Plus the previous shot shows both white rooks still standing in their original positions on the board. (00:15:55)
Answer: Vasek Simek.