Here 'from scratch' probably means 'from fundamentals', e.g. without a prefab game engine, as opposed to 'taking no inspiration or lessons from anyone else or using any library code written by other people'.
> “If you wish to make an apple pie from scratch, you must first invent the universe” :)
This is something I posted on Casey's first handmade video, together with some counter arguments to his rant on the shortcomings of c++ and windows. He has since disabled comments.
Though that would be one hell of a project.