He's not selling prints and these are not artwork he's using at his job, these are paintings he makes for fun, not for sale, he credits the reference/inspiration/ textures he used for the image.
The best way to learn is to study other peoples work and try to make something like it yourself.
He's not a thief or any of that. People can't stand a little success someone's got and them they're selves don't I guess, doesn't bring you far though. Keep your eyes on your own growth and career.