They’re not creating a shadow account, you’re literally logging in with your instagram account.
What this post is implying, is that the user numbers are just existing instagram accounts, which doesn’t make sense because in that case they’d have 2 billion users within the first second.
You can follow/request to follow before the user has actually "created" the account, so they’re lying about which users have done that already, not about how many users they actually have.
This is the moment the account is made. Even if the other person doesn’t respond or has even created an account. That’s how they are driving up their numbers.
So long as you have an account you could potentially have a Threads account without your knowledge.
I hate meta just like the next person, but I‘m not sure how that’s supposed to boost accounts, since you’re literally just seeing these once you already have the account.
They are of course using their advantage in providing you your existing following list
/followers. And they’re definitely happy to push it, but this post is implying something that strikes me as plain wrong.