It's closer because vi was built on top of ex -- vi's ":" commands are just ex commands. In fact, on my Linux box, /bin/ex is just a symbolic link to /bin/vi:

    $ ls -l /bin/ex
    lrwxrwxrwx 1 root root 2 Oct  2  2017 /bin/ex -> vi

The original code for vi was written by Bill Joy in 1976, as the visual mode for a line editor called ex that Joy had written with Chuck Haley. Bill Joy's ex 1.1 was released as part of the first BSD Unix release in March 1978.[1]

(Bill Joy went on to become a co-founder of Sun Microsystems.)

"ex" stood for the extended version of ed.

[1] https://en.wikipedia.org/wiki/Vi