Well explainedWarning: I haven't watched the latest episode.
Viaan has been having troubles trusting women romantically. He doesn't really hate women in general, but is afraid of a heart break. All he has came across women who are more interested in his status rather than him, as a person. In this situation, had they shown Viaan getting involved with Katha romantically that would be out of character for him. He has been fighting his attraction towards her and that's where the ONS test comes. He knew that Katha would either pass or fail. If she passed he would no longer fight his attraction and try to build a normal relationship and if she failed he would convince himself that she was a gold digger like others and move on. But Katha does the unexpected. She goes ahead with ONS, gets the money but still can't afford to get comforts. He can't make sense of it, which is why the Kyu question bothers him. The kyu is extremely important (in his opinion) because his pass or fail depends on that.