The article should have read that you should report one unit of 99211-99215 (Office or other outpatient visit for the evaluation and management of an established patient ...), not 99218-99220, for Friday (keep in mind that the observation unit is technically an outpatient, not an inpatient, place of service).
You should only report one unit of 99218-99220 per observation stay because these codes are for initial care. For subsequent observation care on a day that doesn't involve a discharge, the outpatient care codes (99211-99215) are appropriate.