That could simply mean that he disagreed with the outcome and is expressing that disagreement by quitting.
EDIT: Derp. I was reading the note he wrote to OpenAI staff. The tweet itself says "After learning today's news" -- still ambiguous as to when and where he learned the news.
It is:
> As a part of this transition, Greg Brockman will be stepping down as chairman of the board and will remain in his role at the company, reporting to the CEO.
https://openai.com/blog/openai-announces-leadership-transiti...