Keep an eye on those two

They would be followed because of how they look, not because of anything they did. Young Black people notice this at once, because it happens to them all the time. It is discrimination, and it is poor service.

The question makes Dean look at his own reason, and he may find he does not have one. Greeting them as normal is good service for anyone. Friendly attention is also what actually deters theft.

You have not acted on his suspicion, which is good. But Dean's assumption stands, and he will act on it next time. The boys also get no welcome at all, which is its own kind of message.

You have named it correctly. But saying it in front of the customers turns two boys buying jackets into the centre of a scene. Ask the quiet question now, and raise it properly with Dean or a manager afterwards.