As it turns out, he simply uses your IP and User Agent string. See https://github.com/lucb1e/cookielesscookies/blob/master/inde...

No E-Tag tracking is taking place, since the E-Tag is never send to the server for the index.php request (only for the image request). In theory he could update the session after your IP changed, but he does not seem to do that (the image requests hold on to the old E-Tag).

So, basically, to me it seems like the whole point/post is invalid. Please correct me if I'm wrong.