> " 'Why not?,' I asked."
> " 'Because 'native' refers to the language you spoke as a child,' she answered with a tender, patient look."
Most people think of it like that because it's accurate in like 99.999% of cases, but that's not what "native speaker" means. It's more like, "is fluent and only learned through immersion, not from a class or relating words to another language" - which is how all children learn their first language, but is far less common as adults.
So native speakers mostly learn through memorization and internalizing grammar over a long period, instead of explicitly learning the rules of a language. That's why "prepone" is confusing - native speakers don't learn "postpone" as "post + pone", but as a single unit, so in an area where it's not a normal word, "prepone" is far less likely to be interpreted as "pre + pone", and more likely to be a new word entirely.
(Aside, reading the comic before the article, I paused on it and tried to figure out what it meant. I was thinking some odd local version of "prepare")