Rust Lifetime question

lifetime.rs

fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {
    if x.len() > y.len() {
        x
    } else {
        y
    }
}

fn min_length_string(x: &str) -> &str {
    // Why does this not violate the lifetime checker?
    // Isn't it dropped in with this stack frame?
    // Answer: https://doc.rust-lang.org/nightly/rust-by-example/scope/lifetime/static_lifetime.html
    let string2: &str = "too short";
    return longest(x, string2);
}

fn main() {
    let string1 = String::from("hello");
    let result = min_length_string(string1.as_str());

    println!("The string is '{}'", result);
}