This is essentially what I did using bfg tool. They still took it down.

https://help.github.com/en/github/authenticating-to-github/r...

I'm saying the blob was in a new repository, you had no control over. You couldn't have removed it, you could only make sure it doesn't get referenced in _your_ repository. Which is what you did.

sure, but I imagine they have already removed those forks too.

Have a look at this list https://github.com/github/dmca/blob/master/2020/01/2020-01-2...