R/S is also heavily influenced by Lisp. Haven’t written it in 10 years, but AFAIR it even has proper macros where argument expressions are passed without evaluation.
Didn't they take their array programming from Fortran? The Fortran, numpy and matlab array syntaxes are basically identical, down to broadcasting and reduction rules.
I feel that the article should have made this a lot more clear - as so many people code along the APL -> Matlab / R (via S) -> NumPy family tree.