I’m not sure that’s a given (does Nintendo publish its methodology anywhere?) but in any case, sales charts are not cumulative, well they shouldn’t be cumulative, that would be dumb.
Even if they did count, almost all of those ‘sales’ would have landed in the first few days of the launch which was over a month ago.
All those sales will have now dropped off the charts if they are weekly, fortnightly, or monthly and what you are now seeing is a more natural churn of new console sales (MKW bundle) and existing owners buying stuff from the eShop.