How does someone do animation without using video references?

Hello everyone recently I came across a video on Twitter of a sonic and Shadow animation that was very well animated and very good looking I was able to message the person who made it I want to ask for their process (I am a beginner learning through the animation) they revealed to me something a bit surprising he told me that he imagines the scenes and his heads or sometimes ask them out (no video references).

I wanted to ask how this was possible and if I can learn this as when I entered into this I was told that I would need to be using video references a lot I relying on them