[hncomment]

The delusion that many people are actually one person recurs in mental illness, there's probably even a name for 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.