"decided" versus "have decided"

(Grammar Questions I Couldn't Answer)

With apologies, this is another question that I think I came to an answer on the end.  But I thought I'd through it out to the Internet for a second opinion.
After class, a student of mine came to me with a question he got from his grammar exercises in high school.  (I'm currently teaching in Vietnam, so this was part of what he was studying in Vietnamese high school.)

The text read:

I have changed my address and I live in Corydon now.  I ________ that I wanted a change from Central London because it was so expensive.

In the blank, the student had to choose between "decided" and "have decided".  He chose "decided" but his teacher (also Vietnamese) had marked it wrong and wrote "have decided".

"have decided" made a certain amount of sense to me based on the grammar rules.  The present perfect is used for past actions with present results.  The decision took place in the past, but the present result is that he is living in Corydon now instead of London.
And yet, my native speaker intuition was telling me that "decided" just sounded better.
I thought about it for a while, and decided that in this case, the result was not the focus of the second sentence.  Rather, the second sentence was focusing on the reason for the decision, not the result of it.  The result was in the previous sentence.
So, "decided" was indeed the correct answer.

But let me throw it out to the Internet for a second opinion.