【Rust】ChaCha8Rngでセッションを作りたい

use rand_core::OsRng;
use rand_core::RngCore;
use rand_chacha::ChaCha8Rng;
use rand_chacha::rand_core::SeedableRng;


fn main(){
    let mut random = ChaCha8Rng::seed_from_u64(OsRng.next_u64());

    let mut u128_pool = [0u8; 16];
    random.fill_bytes(&mut u128_pool);

    let session_token = u128::from_le_bytes(u128_pool);
    println!("{:?}", session_token);
}

Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.03s
Running `target/debug/sample`
68291255163114295989027254289217915346

いまいち意味わかってないけどすげえ…