Bi and Ridz must think Rahul is damn stupid that he's gonna fall for 'AR r just friends' phase! He has been observing them for ages, even when AR were actually dating... it's just that he thought it'll be a gud idea to ask now... but they totally denied it!
You could tell by his face he wasn't convinced, he'll be keeping a close eye on AR now... which will probably mean more AR scenes as he will have to find out the truth soon