Are we ever going to figure out who Satoshi is? Probably not anytime soon but we can look for clues. Jia was obviously interested in OSS security and fuzzing[0] but my wild guess is that s/he is not a state actor. I would rather assume s/he is a hobbyist opportunistic hacker who got trigged by the thought "If I can exploit this, why not?". I assume he intended to build a botnet and do whatever s/he came up with. The initial motivation could've been like I said opportunism and perhaps technical challenge of exploiting the software.
[0] https://github.com/JiaT75/oss-fuzz