R is one of those languages that looks like it was designed in a vacuum by a very smart person. It has many common, modern PL constructs, but they're expressed syntactically in a way that in no way resembles any other language I've seen. The entire syntactic legacy of Algol, Pascal, C, etc, all are thrown by the wayside. Familiarity with any of those syntaxes felt to me like more of a liability than a help. That's no…
R is a 'rip-off' / open source re-implementation of the commercial S language by John Chambers. (There are some differences in scoping iirc). Haven't many of its 'modern' PL constructs already been used in Lisp (dialects) before?
There are something things which were grafted on to S/R later on. For instance the S4 OOP system was added much later (in S4) and was based on Dylan's OOP system. So there's a case where the GP is correct that it was taking structure from another PL but it's also one which is fairly foreign to a lot of OOP devs