I don't think the original title was the worst part of the post:
Essentials C# framework 3.5 book from Mark Michaelis, errors in code from the book
And I especially don't think your title change was good:
Error using List
In fact, I think the suggested title made the post worse as it said nothing about the actual issue.
If I clicked a question with the title you proposed (if I even opened it because it doesn't sound interesting), I would have expected someone actually getting an error related to using a list and not because of a method missing a return value.
So in this case both of the reject reasons you received are valid (emphasis mine)
- "This edit is incorrect or an attempt to reply to or comment on the existing post."
- This edit changes too much in the original post; the original meaning or intent of the post would be lost.
But had you not touched the title, the "Too Minor" reject reason might have come into play since you left a lot of issues as Aaron has identified.