It was accepted as bug / missing feature.

Then the OP started complaining... that it's taking too long to fix, that ffmpeg developers are not paying attention to his bug... etc, all while ignoring everything said to him

That person is causing all the pointless animosity.

I do agree that it looks like they should not have engaged him on his level by pouring gas on the flames every time he went off the rails. Remaining on topic would have been the "professional" way to go I guess and just leave him to rant alone. They did take the bugreport though and never questioned that it was valid. All of that still does not excuse the behaviour of the reporter.

I think your assessment that developers should not derive any pride from happy users and are merely there to serve a greater good is a bit far from reality. Maybe they should not worry about things like this but then again these are also just people living their lives. This is not a corporate entity where you engage with a PR representative, these are people, doing what they like to do.