You didn't describe the miracle in the slightest. You gave a highly abstract definition of what a miracle is and then, in a blasé phrase, said your brother had a medical problem in a remote place (and I'm assuming he left the island without this problem or at least on his way to recovery?) That is not a description but a newpaper headline.

When people ask you for explanations, they don't want paraphrased definitions and loose outlines of your arguement/story. That is stuff we already know or useless info. By the way your definition has several flaws but let's not get into that just yet. Try to answer these questions as authentically, plainly and specifically as possible avoiding lofty words or religious adjectives if they can be avoided:

What precisely was the problem?

How did you communicate with God about the problem?

When did God perform this miracle?

How did God perform this miracle?

What was the specific result of the miracle?

What about this event is so special that it cannot be explained through rational means?

____

If you answer these questions, then you'd have a description. Remember to do people the courtesy of providing specifics and details when having an intellectual discussion.