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i don't know about the "common" part, but i know a little bit of chinese, and yes, there's a surname "jin," but it's pronounced "tsin" and not with the "j" sound.
I see! Thank you! I thought he was using his mom's surname because he's in Korea, and I've heard that some Koreans are kind of xenophobic and bullies their classmate or schoolmate who's half korean or isn't korean. And since he have a photographic memory they might want to prevent him from getting bullied since it would traumatized him for a lifetime.
Is the surname "Jin" both common in Korea and China? Or even if it's not common, I know the Jin surname is from Korea, but does China also have that surname? Or Did Soojeong used his mother's surname?