I'm assuming it refers to the fact that most simple Emacs-flavored shortcuts work in any textfield. C-A for <Home>, C-E for <End>, C-K to kill to the end of the line, etc. Certain tookits do this on Linux (Qt for one, I think), and I agree that it's hugely helpful.

So I believe non-readline-style shortcuts would refer to, for example, C-A to select all text.

Exactly. I should probably have referred to them as emacs-style as readline can be configured to have vi-bindings as well.