They probably computed them all by their lonesomes. It's not hard to do.
As a test ... if you live in a place where you can see stars at night, go lie in your back yard looking up, at about 10:00 at night. It won't be long before you see a satellite or two headed north to south. That's a satellite in a sun-synchronous orbit, which is the preferred trajectory for imagery satellites (the trajectory is chosen so that it's always the same local time wherever they're flying over, so the shadows will always be about the same length).
India has its own satellites, radars and big cameras, plenty of high tech capabilities, and a whole bunch of really smart folks who can figure out what sort of satellites are flying over, and looking at them.
Believe me ... figuring out which satellites are ours is the easiest part. Covering things up and unpacking them was the hard part.
Can see some stars where I live. Visibility isn't great. Not sure I could pick out a satallite unless I was shown.
I see your point as to why they could.