“Since WHEN is the counter clerk the one whom decides whether or not the business will open that day?”
Since the manager didn’t do it, the employee is not responsible to keep the store open. The employee does not have the authority to open the doors. Since when is it any responsibility of an employee to open or close a store as you suggest? The employee did the one thing he most likely is responsible to do and that is to secure the premises.
It is a quite common occurrence for an establishment to open before the manager arrives.