No other explanation possible: you reversed the wind off direction, i.e. loaded the film backwards.
Though i have yet not managed to do so myself, it appears this happens. When it does, it does because it escapes the attention of the loader that something is wrong. So why would it be odd that you missed the start line thingy?
Remember that you still see the outside of the roll where it is on the spool. You even see the outside of the roll - the place where the start marks are - coming round the rollers and across the pressure plate.
So not that odd that if it escapes your attention that you are winding the spool off the wrong way, you also miss the fact that the start marks are in an unusual place.