Chessmaster fork quiz/exercise

Chessmaster is trying to tell me this is a fork. How is this a fork, exactly?
if white to move nf6
Chessmaster is trying to tell me this is a fork. How is this a fork, exactly?
if white to move nf6
look at the caption

Probably more a double attack than a fork indeed.
Please look at my blog post to know more about forks:
http://chesstrainerapp.blogspot.fr/2014/01/the-fork.html