Yes, that's right. Nobody has the duty to disclosure the security bugs. It's the security researchers' principles, and if they want to follow that, they can follow that.
But don't take it further that the maintainers have the duty to fix the issues. They choose that career, don't make it sound like ffmpeg is forcing them to disclosure. Maintainers don't "deal" with any security researchers about those, and don't put the confidence that it "benefits maintainers" than "benefit researchers", unless the maintainers declare that themselves. In this case there's no patch, no fix, no PR either, just issue-submission. "You have more benefits" are the claims of the researchers who think that their issue-submission contributions top everything else.
Finding and disclosing the security are issue-submission contributions, and that's it. Don't make it as a gift or something. ffmpeg doesn't have the need to find these issues, and they don't pay for it for it either. And vice versa, they have no duties to fix the issues. They don't force the security researchers to find and disclose things. If security researchers want to do it themselves, they can do whatever they want, but stop at forcing duties to the maintainers. The only thing I don't agree with ffmpeg is bringing those issues social while they can just ignore them, that's it.
I mean, i agree, ffmpeg are under no obligation to do anything. (In the heat of the moment i think my previous comment went too far, i would phrase it more, as if you want to be a "quality" software project then you have to respond to real security bugs promptly).
My biggest gripe though is that ffmpeg does seem to value these sorts of reports highly. If i'm reading the timestamps right, they fixed this report within 1 day: https://github.com/FFmpeg/FFmpeg/commit/c41a70b6bb79707e1e3a...
How often do you get your bug reports fixed that fast? When i file bugs in open source projects it usually takes at least weeks if im lucky to get a response. People almost never respond within 1 day. I think that demonstrates how valuable ffmpeg views these reports.
If the report was a garbage report (like e.g. the ones the curl maintainer complains about) i'd have more sympathy, but clearly ffmpeg views this issue submission as valuable. The whole thing makes me think of choosing-beggars. They want the google report but also are trying to use social pressure to make google contribute even more.
If they didn't want google's reports that's one thing - just reject them, but both wanting them while also demanding more is scummy in my opinion. Either accept or reject them.