Hey thank you I could have been more clear, intermediary is the wrong word and thank you for showing me that. I did read the article, and I can't see where it says "tell them". I do see the bold heading "ask if it’s ok first".
"Hey is it ok if I tell your manager you're doing a great job?"
Is a lot more indirect than "Hey, I think you're doing a great job" and pausing for a response and having a conversation about it.
The point of telling the manager is to help the coworker get their next raise or promotion, not for the manager to be the one to tell them.