> I very much doubt that.

You can see his actual workflow on his YouTube channel. He shows his painting process there but doesn't show his sketching process, but I hope that you believe that people are able to draw from imagination at least.

https://www.youtube.com/watch?v=7_ZLBKj_UlY

> Note sure what you are implying here, could you elaborate?

I just meant I was probably putting to much effort into an online discussion.

> I have no doubt that he started painting these over the reference photos, and then used the 'warp tool' in his painting program of choice to alter the proportions, a very common technique.

It's simply not a common technique at all. I'm not sure why you're making these statements because it feels like your knowledge of how illustrators work is extremely limited. I've heard of people photobashing -- which is when artists combine photo manipulation and digital painting to more easily produce realistic artworks. It's got mixed opinions about it and many consider it cheating but within the field of concept art it's common because it's quick and easy. However, there's huge amounts of people who can just draw and paint from sight or imagination. There's the hyperrealists who often act as a human photocopier, but artists who do stylized art of any kind are just people who can draw from imagination. I'm not sure why that's something you "very much doubt" to be quite honest. Just looking on YouTube for things like art timelapses, you can find huge amounts of people who draw entirely from imagination. Take Kim Jung Gi as a somewhat well known example. That guy was famous amongst illustrators for drawing complicated scenes directly in pen without any sketches. But there's really plenty of people that can do these things.

You seem to be under the impression that the average artist uses every shortcut available to get a good result, but that is simply not true. Most artists I know refuse to do anything like photobashing because they consider it cheating and because it isn't how they want to work, nevermind directly drawing on top of things. Drawing from sight isn't uncommon as a way to study art, so in case you're wondering why Sam Yang would be able to reproduce the frame so closely, it's because that's how artists study painting.

> Have you ever used programs like Photoshop, Krita et al

Yes, very often. The thing is: Just because it's possible does not mean it actually happens.