If the author of MediaCoder uses someone else's software, it's quite reasonable he obeys their rules for that software. He obvisously didn't read the licence for the software (even when asked multiple times). He even makes claims about various software being in the public domain.
Seriously the ffmpeg authors are quite within their rights to be rude to someone VIOLATING THEIR COPYRIGHT. You make it sound like MediaCoder author is the injured party - he is not.