He cannot act on behalf of the entity that owns or operates the store...
Of course they can. They do it all the time. Owners are not always present and employees on duty take the place of the opener interpreting policy, making exceptions, answering customer complaints, safely removing cash and checks, filling shifts, sending people home earl, and calling the police on shop lifters and other criminals.
The clerk wasn't interpreting policy. The clerk was making policy.
Sure. He "could" have ejected the customer, just on the whim he expressed. But, he'd have to accept the consequences. As would/will the owner.
It's been reported that the clerk has, indeed, been fired. So, does the clerk have standing to sue the employer for an unfair dismissal? After all, the clerk was simply enforcing private property rights, in the absence of the owner.
That is simply a matter of trust on behalf of the owner. The employee can be fired if he makes a wrong choice. More to the point the owner may be sued for the stupidity of the employee. MAGA has lost not a thing for standing up to the SJW.
You have a reading deficit I see.
An employee can act within the scope of his employment. A store clerk cannot create or modify store policies. That is why they get fired for doing so. Just because you comply with every directive you get from a pissant clerk does not make it a requirement.