Most of them (as it says) are words the users used once and inserted into their auto correct at an earlier date. When they type a similar word later like "shattered" > "Shatnered", the phone usually auto corrects to the one you added before the pre-programmed list. My old phone used to do it all the time!
I had one at uni with my flatmate jordan, we were in the same screenwriting unit and on a project in pairs, we had to present a half-hour comedy pilot and an essay on the creative process. I was working at the uni library and he was at home. We arranged to meet to hand it in and my text "ok, so me = essay, Jordan = script" came out as "ok, so me = essay, Korean rapist".