Nice to have another point of view (no offence jan Kipo).
Unfortunately some Toki Pona speakers use their own slang. The best is to ignore these people.
Ah slang, what a wonderful thing. If I have not already begun using my own, then I am sure I will at some stage
"mi jan Natan." is correct because "Natan" is not a official Toki Pona word. To make it clear what it is we use a noun before. The word "jan" show us "Natan" is a human. In "pu" unofficial word are adjectives and need a noun before. But Sonja use in pu the example "nimi mi li Apu" also. From the grammatical point of view it could be correct (NOUN + li + ADJECTIVE). The adjective belong to the noun here. But this unclear because "Natan" could be a name, a disease, property, ... (sorry .
As I see it, if I was asked: "Who are you? (sina e seme?)", I would think my answer could/should be "mi jan Natan.".
Alternatively, I might answer the question mi e sewi pimeja (attempt at saying "I am the dark lord") which states who/what I am, but not my name (so much), or mi e ilo mije (attempt at saying "I am the tool man").
However, if I was asked: "What is your name?" (nimi sina e seme?), I would think my answer should be "nimi mi li Natan", as I have been directly asked what my name is—so I should directly say what my name is.
Am I alone in thinking this?