The app id (com.facebook.stella) was for an app called Meta View. It looks like they just rebranded an app that was previously used for Smart glasses and is now using it as their official AI app.

Why rebrand rather than create a new app? Who knows. Maybe to demonstrate a high(ish) download count at launch, maybe for app/play store credibility.

They rebranded the app designed exclusively for that (Meta View) and added the chat features.