Such a vindictive guy! This was the second time Sajid tried to manipulate Sumbul by asking her to go and hit Archana. First time it felt like he was just joking, but saying it for the second time to the same person, that means he really wants Sumbul to get physical with Archana. He thinks it won't look bad to the audience because he's asking one woman to hit another woman.
That is why this guy was acting like a caring uncle of Sumbul. He just wants to use Sumbul for his own selfish purpose. He knew Sumbul is having a very weak moment, and she's very desperate to get evicted. It was very much possible she would take his advice to get out of the house. Such a jerk he is.
He also knew Sumbul is the only woman in the house who would fall in his trap, and she very much did. Fighting with Archana for Sajid was so stupid. You have bigger issues to worry about Sumbul. First learn to fight your own battles, then fight for others!