Never thought to think about it this way - back in the day I just assumed they are most likely just trying to get more visibility with the news of the app going behind a paywall making conversation - and then later playing the "ok you win -card" and reversing the decision (with the customers are more important than money feels). Though back then there was no Signal or any other real mainstream usable alternative, and also Zuck hadn't bought them out yet I believe.

But you might be right, if the snowball was about to go out of control this would have been a smart way to throttle growth, a little uncertainty would do the trick and is also conveniently quickly forgotten without significant PR loss. Good angle!