Perhaps the Silver Woods HOA agreement requires emergency phone numbers and Stander had Carl's number on file? Or,more likely, OP/Carice simply gave him the number?
Now that you mention Carice, who actually did talk to Divaris and Carl - Carice, OP or both?
Whatever the answer, the fact remains that Divaris was called before Carl.
According to Carice, she noticed OP was busy on the phone but wasn't making sense. She took the phone and told the person at the other end (she doesn't know if it was Justin or Jason) to come over quickly, OP needed them, he had shot Reeva and that she was dead. She then phoned Peet van Zyl and Carl. She "spoke to Peet from the beginning". The phone was in the kitchen and she believes it was plugged in, on charge. She later saw a cell phone in the garage on charge but can't say if it was the same one.
According to OP, Carice asked him if she should phone anyone. She called Justin but he doesn't recall whether he spoke to him (and therefore what he may have said). She phoned his agent Peet van Zyl, and his brother Carl "if I'm not mistaken".
Can't find anything yet on who spoke to Carl.
Notice that the sequence of the calls doesn't tally with the phone record, which shows a call to Carl before Peet. Nel even corrects himself to state the wrong sequence (Peet then Carl) when cross examining Carice and she agrees that's the sequence. He asks if OP made or could have made any other calls and at one point establishes that Carice went outside briefly. She also told Roux that she "once or twice went out" before OP was taken to the garage and the scene was secured. Not sure where this was going as we have no evidence of a call to Carl after Peet.