Laravel 5.1 | Issue while handling CSRF / XSRF tokens

I have a very possible silly doubt as I am not used to this concept of XSRF & CSRF, I do know the use of CSRF protection to some extent and currently working on a project, I came across this piece of code in the Laravel 5.1 VerifyCSRFToken middleware which is built in, I have a a strong doubt in below line of code.

protected function tokensMatch($request) {

        $token = $request->input('_token') ?: $request->header('X-CSRF-TOKEN');

        if (!$token && $header = $request->header('X-XSRF-TOKEN')) {

            $token = $this->encrypter->decrypt($header);
        }

        return Str::equals($request->session()->token(), $token); 
}

Why is CSRF token is being matched for just a session token while XSRF is being decrypted as a encrypted string , I caught this doubt since my XSRF token is generated using just Session::token() method , But while the next post request the X-XSRF-TOKEN carries that token and lands on this middleware where that is decrypted and throws a Invalid Payload Data error with an exception :(

via Chebli Mohamed