fn new_session returns wrong type?

[KyleSebion]

Not sure if this is the right place.
I was reading https://www.shuttle.dev/blog/2022/08/11/authentication-tutorial.
I saw that fn new_session is declared to return a String but seems to actually return a u128.
I tested similar, but simpler, code at https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=7f53177c59d32f1e9ac8a908c69bc9e6 and it gave an error.

The following seems to be the same fn as at shuttle.dev:

shuttle-docs/templates/tutorials/authentication.mdx

Line 492 in e73774f

pub(crate) async fn new_session(

Am I reading/doing something wrong?