Fair comment, thought something similar when I first read this, but ML falls into its own category IMO because it's not part of the "application" most of the time. It's back-end in that it's not front-end, but it's not what you'd normally consider the back-end of an app.

A model is built offline, experimented upon, tested, and then once ready "connected" to the main app. Like, the TensorFlow code you write doesn't "need" to be on the server; it could be running on your laptop for all you care. It's the output model that eventually makes it into the back-end ¯\_(ツ)_/¯.

> Honest question: does "back-end" now mean "the CRUD and API client portions of a web-based CRUD app?"

Back-end has always meant the CRUD/API portions of a CRUD app.