- Edited
How do you know it's just an API update? Was there an announcement somewhere?
Anyway, an app rollout can also be done in stages. It is called staged rollout. And if the devs decided to do a staged rollout of the app, it means that only a percentage of their users would see the changes first. Which is a wise thing to do because they may wanna make sure that the functionalities are working correctly before they roll them out completely to all users.
In addition to that, when exactly an app update will be released to the targeted users depends greatly on Google's or Apple's approval. App developers don't really have a say in this. They can submit their update, but Google and Apple still have to review and approve it.
Also if a user has an auto-update on, then the app will just be updated without them knowing.
Just wanted to make sure, hence I asked for his/her app version.