I think the difference is that Twinflames stay but not for too long. They always walk away or run which is not necessarily toxic but karmic stay in your life by some kind of force or manipulation to do toxic things to you.

They both do hurt.

The twin flame is a cute kind of hurt that makes you sad to help you love yourself lol but the karmic is a toxic kind of hurt that makes you sad, angry, sick, distressed, everything to get you to learn haha