On the lessons that teach how to move the pieces only one of the possible moves is correct while all of the others are alternate correct moves.
I'm not sure what you're asking, but yes. This is done to drive the main idea of the paticular problem. While the continuation you saw would lead to an equally strong position, it may not prove what the author is trying to teach, or at least not demonstrate it as well. It can get very annoying, especially on some of the problems that have several "alternate" moves, but it does serve a purpose.
Thank you for your help. I'm still new to this site and learning how to use Chess Mentor.