That's not exclusive to that app. Being able to update the app without going through the App Store was one of the big selling points of React Native a few years back. Apps are not allowed to download native code, however.
You cannot download and execute native code on iOS, the sandbox prevents it. Memory protection ensures that pages marked as data cannot be executed
There is a special entitlement to allow some Apple apps and frameworks to do this — Apple’s JavaScriptCore can do JIT, which requires executing data pages. Similarly, Swift Playgrounds can compile to native code and execute that code
So, for example, you could ship a C compiler on iOS and it would compile perfectly valid binaries, but you would never be able to execute those binaries natively without code-signing them and deploying them in an Apple sanctioned way, which you cannot do on-device (except with the above mentioned exceptions)
That's ...not a feature of React Native. It's possible to reload the app's content on code change, but this very clearly intended for development only.
You’re describing fast refresh, the parent is talking about codepush. The whole point of CodePush is definitely to update the app without going through the store. It downloads a JS bundle (which is usually most of the app functionalities) and executes it.
There is a special entitlement to allow some Apple apps and frameworks to do this — Apple’s JavaScriptCore can do JIT, which requires executing data pages. Similarly, Swift Playgrounds can compile to native code and execute that code
So, for example, you could ship a C compiler on iOS and it would compile perfectly valid binaries, but you would never be able to execute those binaries natively without code-signing them and deploying them in an Apple sanctioned way, which you cannot do on-device (except with the above mentioned exceptions)