What is Twig For Drupal?
Twig for Drupal 7 is an implementation of the Twig template engine for Drupal 7 (duh).
The development of this implemenation was done before the decision was made to make Twig the default template engine of Drupal 8. Therefor this implemenation is NOT a port of the Drupal 8 version.
However you can use the same tricks like you would do when writing a theme for Drupal 8 in this Drupal 7 version. I think it is even a rather clever way of future proofing your site NOW, if you want to migrate to Drupal 8 later. Most of the template code can be straight ported to Drupal 8.