If Black takes the Knight, White plays Qxd8+ Kf7 0-0+ Nf6 Qc7 and White will win even more material. Instead of Kf8??, Black could play Nc6 and have a playable position.
I have to say that I really don't understand black's annotations for this game. Early in the game, black laments having to play a "book opening" since they are not interesting. This is already strange. Book openings tend to be the most interesting way to play, that's why the GMs are playing them. Then later in the game, black is overjoyed to play a well known opening tactic and finish the game without playing a single new move. What was supposed to be so interesting about that?