I wonder if it's more a question of that they might "be angry" (professional or not the emotion can come anyway) but what they then do with it?

Some might feel a moment of anger if you reject their advice for example, especially if they believe that the advice you follow instead is harmful to you and that their advice would have led to healing. So that the anger is really out of concern for you; and yet, they need to be able to express that in a way that is kind, caring and professional rather than any kind of lashing out, hurtful response.

Or they may be angry with a choice; but not with you, and again, the main issue would be what they do with their anger?

So anger the emotion could be present; but what the T does with it in the therapy environment should be "professional"