Yes, it appears you are right. I have adjusted the last commentary to make more sense. However, the goal of the lesson is really to learn concepts and practice the fork tactic which this lesson does show.
Error in Champion Tactics with GM Wolff - Forks-Lesson 8?
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After the solution moves, isn't the D7 knight lost? After the attacked F8 rook moves and any white move, RD8 attacks the white knight which has no safe squares to move to.