Dak
mentat
You can't separate those two things and make following policy the bottom line with no ulterior motivations. That's not how bias works.
Why would she enforce the policy for two black men and not for white people? Maybe she just dislikes them so much that she uses the policy as a means to stage her prejudice--in which case, that's bias in asking them to leave. Or maybe she unconsciously feels that two white people sitting down without buying anything aren't likely to be dangerous; but two black people sitting down without buying anything might be planning some kind of violence--in which case, again, that's bias in asking them to leave.
The bias enters into play when someone acts differently than they normally would. Just because something is policy doesn't mean it reflects some baseline of standard behavior. For example, it's policy to drive under the speed limit (that's why it's a "limit"), but people regularly drive five to ten miles-per-hour over it and don't get pulled over.
Again, we don't have counter evidence that enforcement has been different. All we can somewhat safely assume is that no prior situation has escalated to the point of police being called (based on a lack of customer responses/complaints/media coverage), and we can safely assume that these are not the first two black customers the store ever had. Making a ton of assumptions over a single incident where the customers were equally willing to escalate the situation despite numerous requests to comply with a reasonable, non-racially based policy, seems to me to be a form of base-rate neglect and special pleading.
We can both agree the policy for the store is probably a poor one, although I hold the caveat that nonpaying occupants are social miscreants.
A better example of bias people should be focusing on is how the Tennessee shooter had multiple incidents prior to the shooting, and yet the police either let him carry on or weren't even called. We can be reasonably sure that would not occur with a black or hispanic person.