Because he wants you to move and develop a knight,not a bishop.
Bug [ ]: Game Review move explanation names wrong piece, knight instead of bishop

Because he wants you to move and develop a knight,not a bishop.
Look at the position. The knight is already developed. The best move is with the bishop as shown in the first line displayed, Bf5, and the board position,

I've had the same problem with it calling my Knight a Queen once. I'm not real tablet savy so no pics, but it has happened more than once. A piece that's already developed, it telling me i missed an opportunity to develop a piece that's already developed. Hopefully next time I'll be able to screen shot it. Unless I'm misunderstanding something. But it definitely called my knight a queen, referring to the move, on the right square, just wrong piece.
From https://www.chess.com/analysis/game/live/65337622949?tab=analysis