I've only heard once a feedback about my commits on Github and that was “I've checked you out on Github, cool, the other applicants didn't even have projects on it." Maybe it's a German thing, or maybe this guy is living in a bubble.
I had one particularly tech-savvy CEO personally reach out and try to recruit me because of my open source work. My project wasn't directly related, but he recognized the similarities between the problem domains, and that impressed me. But his wasn't a financial firm.
I can't imagine any tech-centric organization being hostile toward open source contributors, whether they're an investment bank or not. I could maybe see it on teams that aren't tech-focused and are led by old-school business types who just don't "get it". But teams where tech is their biggest asset, like electronic trading? No way. If you run into this sort of thing when applying for jobs in the financial sector, you're looking at the wrong jobs (or the wrong banks). Look for roles on electronic trading teams or HFT. The work is more challenging, and the compensation is better anyway.
Better still, apply at Susquehanna or Two Sigma, or some other place that really recognizes the value of their engineers. Stay away from huge banks like Citi.
I agree. Personally I couldn't imagine working at a company that was hostile to my open source contributions, anyway. If I was contributing to something controversial, maybe.
Of course that's a reaction coming from privilege: I can afford to turn away potential employers like that. Maybe my Github profile has turned people away. If so, I don't see it as a loss.
On the other hand, I've fairly regularly gotten contacted by recruiters pointing out they've seen I have a variety of Ruby projects on my Github, for example, so overall I'd be surprised if it is overall a bad thing for most people.
Banks are indeed one of the most secretive and protective institutions, along with a lot of other related ones in the financial sector. They also tend to have more authoritarian practices, which can explain why they're not so keen on their employees doing even remotely-related stuff outside of their work.