I don't think that Redis qualifies as a large software system in the modern standard. In fact, it's popular because it's simple, small and understandable compared to its competitors which comprises of many millions of lines of code.
Redis is ~200K lines of C code, so it's relevant project-size-wise, but - redis was started in C, right? It's not like developers now have the option to "go C++" without a company-wide decision.
Still, if could quote Redis developers making the GP's claim, that would count.
Redis is written entirely in C.