That's the first I've ever heard anyone say that Stallman had anything to do with Tcl. Do you mean to imply that guile wouldn't exist if Tcl was GPLed? Or something else?
I'm not entirely sure about that. While Stallman is most famous for his license preferences, he has a longstanding, pretty strong pro-Lisp preference as well, dating back to his early work on Emacs Lisp. Guile Scheme was created as the official GNU extension language mostly because Stallman thought a version of Lisp was the right language for a standard GNU extension language, and Tom Lord convinced him that Scheme was the right version of Lisp for the job. It wasn't a preexisting GPL'd interpreter that he just picked because of its license.
https://news.ycombinator.com/item?id=12025218