The bug post is clearly from a developer who I assume is a bit desperate to fix an issue. He certainly isn't representing Microsoft in the bug post - I assume he was naive and thought mentioning Microsoft would bring attention to the issue (it did, the wrong kind).
There's no information about the "offer" Microsoft made, but I'll take a guess: we have an initiative that selects through voting open source projects that are awarded a one time payment of "a few thousand dollars". Unless evidenced otherwise by ffmpeg, I would assume this is where that money is coming from.
A company as big as Microsoft has lots of procedures and bureaucracies involved in contracting with third parties, and I don't think they were aiming for a support contract in this instance, or, at best, someone looking for help found a simpler way of paying out, instead of going through the proper channels.
People tend to see big companies as an entity of their own, instead of a bunch of people running different processes around.
I think the lesson here is that we need to educate our developers on how to communicate with open source projects and third parties.