You're benefiting from elision. Modern Rust lets you omit mention of a lifetime when there's only one plausible choice. So, often today you can write Rust that doesn't mention lifetimes but they're implied.

But it wasn't always like that. For a while Rust would insist you spell out that OK, this function parameter has some lifetime 't and the function result also has a lifetime 't. Now, Rust says well, the result needs a lifetime, and your function takes one parameter which also has a lifetime you didn't specify, so, the plausible explanation is that they're just the same lifetime, let's assume that's what you wanted and only complain if that won't compile.