this doesn't make sense
It most likely doesn't,
but think of it this way, 1000 posts is clearly enough evidence to tell if someone is just an alternate account because their past behavior would have shown by then. At least, that was my train of thought when I wrote the thing.
The first one does, though. I've seen so many times where a person will make a sort of "Hello World!" post and within the first page someone usually (probably jokingly) asks if they're an alt.
Why are people making a bunch of achievements about being banned? That seems counterproductive.