The lifetime syntax was taken from OCaml but it has somewhat different semarics than OCaml. I honestly get a bit tripped up when I look at OCaml code (a language I'm a beginner at), and see ordinary parameterized types using syntax that suggests to me, from a Rust background, "woah, complex lifetime situation ahead!"
I know that Graydon Hoare is a fan of OCaml and that it was a core inspiration for Rust, and I sometimes wonder if he gets tripped up too by having to switch between Rust-inspired and OCaml-inspired interpretations of the same characters.
It's similar but different: both are type variables, but it's true that it's used for the "other" type variables in Rust.
For what it's worth, I am not even sure that Graydon was the one who introduced lifetime syntax. He was a fan of terseness, though: Rust's keywords used to be all five characters or shorter.
I know that Graydon Hoare is a fan of OCaml and that it was a core inspiration for Rust, and I sometimes wonder if he gets tripped up too by having to switch between Rust-inspired and OCaml-inspired interpretations of the same characters.