Kind of surprising, since Stallman was a developer with and user of Lisp Machine Lisp, the single biggest influence of Common Lisp.
Maclisp and its successor Lisp Machine Lisp, were probably his biggest influences. Emacs Lisp is based on Maclisp - without the features of Lisp Machine Lisp like keyword arguments, Flavors as the object-system, ...
I code in C regularly, yet I do not care and am not interested in C after C90. Only some library features of C99 and that's about it.
Stallman's concepts of what is Lisp, how to use Lisp, how to implement Lisp, were formed long before Common Lisp.
If you're in that position, it's easy to have allergic reactions to requirements you don't agree with.