The diagram is correct. It’s not legal, but it’s correct! It’s a task problem by Shinkman. Your task is to make ten white moves (the bishop stays on the dark squares) to create a position where Black, by putting a knight on the board can checkmate White with that knight placement.
This would be good fun for kids learning the game. Hope you had fun figuring it out: 1.Kg1–f1 Kf1–e1 2.Ke1–d1 Kd1–c1 3.Kc1–b1 Kb1–a1 4.Qh1–b1 Rg2–a2 5.Bh2–e5 Be5–b2 And the knight plops itself down on b3.