There is no threat model for an iPhone app to do nefarious things in an App Store distributed app on a non-jailbroken phone. At most, FaceApp grabs the picture you uploaded and some minor meta-data that every app using an analytics tool (read: all of them) collects. This is political grand-standing at best, and would be a non-issue if you replaced the geographic location of the dev team with any other countries I get…
By "non-jailbroken" you should mean "jailbreakable": it is the existence of the vulnerability that makes the phone insecure, not the user having used an exploit to leverage that vulnerability to do something for them. Like, for no avoidance of doubt: if you are running a version of iOS for which you can download an app-based jailbreak (which has been all jailbreaks for current phones that have been released for years now, all reliant on sandbox escapes), the issue is that the attacker jailbreaks your phone, not that you do; and also, to be explicit, as people also often confuse this, the code I would put in an app for a "back door" capable of letting me jailbreak remotely would not look like exploit code but would look like an innocent bug: maybe a vtable use after free bug on my stack while parsing a network response for which I knew the location of all the required ROP gadgets to exploit (put different "if you want to put a back door in software, just leave yourself a vulnerability you know how to exploit, and then claim you weren't evil, you were just bad at memory management or concurrency... like everyone else).