Hi UmairAftab,
About 3 weeks ago, you were asking about how to properly train for RC. Have you been practicing those skills during that time? If you have been focused on properly 'attacking' prompts as you read, taking effective notes and honing the necessary skills needed for each sub-type of RC question, then this recent improvement might be the result of the work that you've put in.
The scoring algorithm on the Official GMAT is far more complicated than most people realize. Since that algorithm is proprietary, no GMAT company has an exact match for it, thus CAT scores can vary a bit based on the 'biases' involved in their respective designs. While the most realistic CATs available are the 6 from GMAC, the CATs from Kaplan,
MGMAT and Veritas are all 'close enough' to the real thing that they will provide you with a relatively realistic score assessment (assuming that you correctly take the CAT in a realistic fashion).
How did you perform on the Verbal section overall? With an adaptive Test, your performance on the ENTIRE section will impact the difficulty levels of the RC prompts that you receive. If those prompts felt "easy", then you might want to review how you performed in CR and SC.
GMAT assassins aren't born, they're made,
Rich