It is not that simple, you maybe did not spend enough time analysing it.
They are a mix of handpainted style and based on photo/real life texture. It looks like, for some at least, they used some photo/real life texture, apply some filters, and paint by hand on top of it.
And they have normal maps by the way, at least a big part of it baked from hi poly sculpts.
They seems to have a very organic "chiseled" style. And their proportions and faces are fairly stylized. While stylized, there is still an enormous amount of detail sculpting into faces and what not. While the texturing is important to achieve the look, the sculpt is equally if not more important so you should start there.
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They are a mix of handpainted style and based on photo/real life texture. It looks like, for some at least, they used some photo/real life texture, apply some filters, and paint by hand on top of it.
And they have normal maps by the way, at least a big part of it baked from hi poly sculpts.