Business logic usually exists in a mobile application for the same reason it exists as client-side logic/scripting on a web page:

To reduce latency and improve the user experience.

In a comment you mention banking applications, and that's something with which I'm fairly familiar, so let's go with that.

Selecting specific from or to account types--or even specific combinations of both--can trigger specific changes to the UX and affect validation requirements.

Different legal disclosures might need to be shown or hidden, or the minimum payment or transfer amount could vary and require real-time, on-screen validation before submitting a payment request.

Enforcing those requirements without continual round trip API calls to the server places those business rules within the client.

And that is "business logic", regardless of your attempt to recategorize it.

I might also mention that what's terrifying to me is a developer who continually uses the word "never".