First, to be clear, the close item you are seeing in the timeline is not your flag. It is a review task which was created based on your flag. Your flag is currently still active, but may eventually age away if no action is ever taken with the question. You can see the status of your flags in your flagging history by clicking on the number of helpful flags you've raised in your profile.
The review task itself was invalidated because it only had 1 vote or flag on it, and it sat in the review queue for several days and no one ever took one single action on it. Either they were skipping it or just plain not seeing it. In order to keep the queue number down on Stack Overflow, tasks which only have one vote or flag and don't see any action simply get removed from review. If the question ever gets another flag on it, then it will re-enter the close queue with a bit more weight and hopefully someone will actually look at it. The act of these review tasks being invalidated has absolutely no effect on the status of your flag.