Parent stated that some variations drop the 'whole different computing system' part of Lisp; which makes them Lisp-syntax languages rather than actual Lisps. I believe he means things like modifying a class and updating all existing instances without having to restart the application, the continuation/restart system, and so on.

As an aside, please remember the guidelines: 'Please respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize. Assume good faith.'