I think that is untrue. I worked at the Network Systems arm of Bell Labs for sixteen years, and we could demonstrate five-nines of uptime on complex systems written entirely in C.
C is a rough tool, I will grant you that, and Rust is a welcome addition to the toolkit, but saying that most code written in C is horribly unsafe, does not make it true.
https://www.acsac.org/2002/papers/classic-multics.pdf
So not even back then.