More that the company’s culture says you should post things using the company’s platform, and to not do so might be making a statement he doesn’t want to make.
Otherwise, why would he move away from .plan?
Could it be that a lot of people don't know what a .plan file is, or how to read content from one?
If John Carmack started updating a .plan, people would figure out how to check a .plan.
You said 'it wasn't his decision to make' not 'perhaps he wants to use his employer's platform'. If you don't want to imply it's coercive, you should phrase it in a way that doesn't imply it's coercive.
I believe it’s a “perhaps he feels he should be using his employer’s platform”. A murky coercion middle ground.
Ok, but "I don't think it's his decision" is then a weirdly overwrought (or less charitably, thoughtlessly provocative) thing to say. It's totally his decision. Nor do I think anyone at FB would be stupid enough to tell him where to post random ffmpeg things. He's also active on twitter - as you can see in the post we're discussing.
It doesn't have to be coercive. Some of us would like to know what the people who hire us are up to even if we don't personally have any interest in it.