The key is the fine-grained instances (gadgets).

E.g. if you're using a slide editor app, each slide deck you create is its own instance of the app, whose code can be independently modified.

The slide content and the code are kept together and sandboxed together.

Adding HIPPA data to the app is no different to adding it to the slide content. I suppose whether or not that is OK depends on a lot of things, but the same things apply to traditional PowerPoint. The fact that the code is modifiable doesn't change the situation, since those modifications are sandboxed and constrained to that one slide deck.