Hello student,
The rank predictor in based on the previous year's trends. It cannot be 100% accurate as well as 100% false. They are just predictions, as scores and ranks vary each year depending on the toughness of the exam, availablity of seats, state quotas, category and the top neet score. But, you can go through the following link to know about the cut off's and ranks for the previous years and calculate your chances of selection in neet ug exam.
https://medicine.careers360.com/articles/neet-cut-off/amp
Good luck