Didn’t emacs get developed on ITS or Multics? Seems Unix just imported it, but your point still holds.
GNU Emacs later (1984) was based on Gosling Emacs (1981), which was written in C and extended with Mocklisp. Mocklisp was a rather uncomplete Lisp, which was replaced with Emacs Lisp by Richard Stallman.
Yes.
Emacs development began during the 1970s at the MIT AI Lab, whose PDP-6 and PDP-10 computers used the Incompatible Timesharing System (ITS) operating system that featured a default line editor known as Tape Editor and Corrector (TECO)