Maan has a lot of built up anger in him. Somebody is coming and taking over his life, his house, his bedroom and he is not going to take it all lying down. He is not the one to listen to his grandma and hand over the keys of his house to Geet. Geet the girl who did not want him to even touch her back in Hoshiarpur is now fighting to stay in his house, in his bedroom even throwing challenges at him. It is affecting him big time. And I guess this confrontation was needed for Maan to understand why Geet is doing all this..... and Geet needed this kind of words to get back to reality and tell him why she is not willing to go out of the house.
I am sure after this they will be fine. No need to worry much. Maan will apologise for whatever he said and they both will have better understanding with each other after this episode.
I would like to think that this is just a one-time thing. When the real truth hits Maan, he wouldn't jump to conclusions as he is doing today as by then he would have known at least a bit of the truth - that being he can trust Geet.
Cheers,
Ash