This isn't pretty. Gwern doesn't look good here, messing with someone that was clearly mentally ill. Even at the end when he breaks this opinion he positions himself in a smugly superior way, insincerely offering this analysis.
Kids go through crazy phases and still mature into stable, reasonable adults.
Edit: To me, the writing style seems very teenager-ish as well, though I don't have a good baseline for mentally unstable writing.
That said, the thought occurred to me that it might be someone aware of how easily one would otherwise be able to match up their linguistic patterns and identify them to another online persona, and that perhaps they were actively trying to combat that.
The former scenarios are completely contrary to the former, and it shouldn't be forgotten that this is all very recent, and not something that concluded years, months, weeks, or even days ago, so it's possible we haven't seen the last of it.
Coupled with insecurity, it might lead to paranoia and feelings of persecution by a powerful puppet-master. Here it seems paired with grandiose delusions, perhaps because the person is otherwise intelligent & high-functioning, or using drugs which create a sense of invulnerability. Either way, there are strong indicators of mental illness.
I would put joking (or trolling) as-if-mentally-ill as a second-place possibility, and teen-daydreams as a third-place possibility. But maybe all three in different proportions.