We will have orientation take place at other stores from time to time, that's the day where you sit in the training room with the human resource executive and watch videos and review the handbook. This occurs most often if the executive is on vacation, or if two stores have hired small amounts of people, allowing the training to be consolidated to one store and free up the time for the other store's human resource executive.
As far as training goes, there are a few explanations, but it seems less common. Maybe the store you are working at doesn't have someone who traditionally trains cashiers working this week and they need you on board right away. It could be an ultra low volume store (a store with much slower sales than average) and they can't afford this week to have someone doing training while the front end is open due to staffing amounts. Or, as has been mentioned before, perhaps your store has a lower score in one thing or another and they want you to train from a more effective place.