That's way too general. An entire company and dozens of people could be behind one IP address.
Sure, if you only try to use it from work that may make ti a bit harder to pinpoint which is why I said among other things. I think we're all aware that browsers leak information about you and your machine if you aren't careful.
You mean they banned the whole hedge fund OP works for?
They're probably seeing a new account pop up and using the ip range along with some machine info leaked by the browser to pin down the OP, or just the machine info.
No.
And also they banned me before I started working for the hedge fund.
Previously I worked at Siemens, we did not use GitHub, we had a self hosted Gitlab instance.