Poor Carlos. His sticking to the rules required to ignore Serena's emotions. They probably instructed him on that aspect of umpiring specifically, to avoid a recent mistake made by Mo with Nick.
But rather than hopefully coming up better than Mo did, Carlos will actually regret his action. Crowd boing him, TD deciding not to give him the souvenir, and now receiving harsh scolding remarks from tennis writers for his "unnecessary and destructive involvement" in the match. Mo is actually smiling now and patting Carlos at the back and saying: "Hey brother, you should not ignore Serena's emotions, you should step down from the chair and give her my pep talk, you should even hug her, and everything would be back on track! Screw the rules, we are umpires but we are also humans not computers!". Except, with Mo's prior experience, not only Carlos but no ump would dare to do what was right to do against tennis rules in this case. What a travesty of justice!
EDIT: Both Mo & Carlos are my favourite umps & I'm sad they strayed into mistakes in their umpiring, in such extremely opposite ways, rather than staying their middle ground and be in control of their matches.