I disagree. You're contradicting a facet of the story. It's explicitly true that the reasons for their actions are not stated. If you then go and state those reasons, you have contradicted that lack of statement.
You can then go on to build a story around another story. Which is how I view series like, for example, Harry Potter. The first book is it's own story, whole and complete. The second book is it's own story, which includes facets and characters from that story, but ultimately is it's own. And so on, adding layers and connections.
Ever heard the phrase 'Watch what you say because you can't take it back.'?
This is no less true for written works. The Author doesn't have true ownership of the story or it's meaning.