I’ve been using vim bindings for a decade and never knew this…

It's about the ascii code and terminal code. (Almost?) Every non-printing character can be entered with Ctrl+<some keyboard key>. With Control pressed, D is eot (end of transmission), G is bell, H is backspace, I is line feed (next line), L is form feed (new page), M is carriage return (start of line), Z is substitute, and [ is escape.