The IITs are funded by the Government so it has complete authority to give admission to anyone. The teachers or the students are not the stakeholders in the case of IITs. It is the Government that pays the teachers' salaries and installs the various facilities. The Government is at complete freedom to decide who can come into ITs and who needs a push in the form of the reservation to join ITs.
The aspirants know beforehand that the Government has set such rules according to its own discretion. No one is forced to give the exam and you can always choose any other option if you think it’s unfair.
Here is a video giving you an honest review of the institute
Aspirants know that there might be cases where a candidate with 10k or above rank will get admission in contrast to the general cutoff. They still fill out firms in hope of clearing the exam. You are precisely giving a Government Exam and need to follow all the necessary rules. So it indeed is justified if someone with a 10k rank is able to make it into IIT Bombay.
Your friend must belong to the reserved category. Securing IIT Bombay CSE with a rank of 10k is only possible if you have any reservations. Your friend must have cleared the cutoff for his category.
For general category students, the cutoff is definitely higher. For 2021, IIT Bombay cutoff for CSE was 66 (general category students).
If your friend got CSE at IIT Bombay, that means he/she must belong to the reserved category. Reservation is good (not caste-based) as it evens out the playing field for the students belonging to this category.
For instance, this friend of yours has a rank of 10k- if he is a reservation candidate, his rank would depend entirely on his category. This arrangement is separate from the normal ranking system. And as you've mentioned, if your friend has secured a rank of 10k, chances are- he might have belonged to a list that's open extended. These students from the open extended list don't save a seat for themselves in IITB CSE. But if he has still managed to grab a seat at IITB CSE too, his AIR must have been >25. Comparing such a candidate's rank to the general category list, it should be around 3-4k.
This incident may not reflect equality, but assuming it was a genuine case, it is justified.