It is drawn on ipad with sketchbookpro app. There’s many drawing apps to ipad, you should try one or two. Many of them are free.
The colors never ends, you can paint in layers and you can erase whenever or whatever you want in the picture. It is a fun way to draw pictures.
Still I like drawings on real paper best. But sketch on ipad is a very good, quick and easy way to try out different versions of a picture you want to make.