That badge doesn't have an earned date underneath it, which means you haven't really earned it. There are examples of this glitch in member profiles. We're not sure why they appear randomly, only that they don't mean anything unless there's adate attached.
Top 0.5% is a category that no longer exists. That badge in your profile is caused by a community website glitch. If/when you earn any type of community reward badge, there will be an indication of when you earned it.
I noticed that I had that badge in my “collection” as well and wondered what it was as I don’t see any reference to anything abouve Top 1% and I’m really not remotely that talkative!