A better number would be that they were able to push 1 in 40 of Meta's users and 1 in 10 of Instagram's users into the app signup in 5 days of national press coverage. I have no idea what typical uptake of a feature is in Instagram. Nor do I know how many people signed up and checked it out vs. became actual active users.
I also am not sure if 100 million users is even anything to be excited about at Meta's scale. Google seems to kill projects that have that many MAU for lack of executive support.
On the other hand, it's common sense for a photography-and-video oriented social media site to support tablets, and yet there's still no iPad Instagram app! (Although there is a minimal browser version.) From that perspective it would not surprise me if they end up staying app-only, as weird as that seems.
badump tsss