Genuine question
Edit: change the title from “Why can Socialist Market Economy be categorized as socialism, and why is NEP categorized as state capitalism?” to “Why can Socialist Market Economy be categorized as socialism meanwhile NEP is categorized as state capitalism?”
My point is state capitalism is not necessarily useless term exclusive to left {anti-communists} like you indicate it is. It’s also a matter of life description.
That being said, fine, market socialist