I have a gut feeling that RK is spying on sultans moves and his tactics and fails his attempts, for sure he doesn't trust sultan as he feels that he will try to break his marriage with madhu.
I've just watched the scene now, RK does know sultan is there behind the tree, that's why he insisted on taking madhu shopping, and yes the way he put his sunglasses on whilst walking past sultan and that sly evil grin said it all. He is way too smart. No one can beat him 😉