He didn't. Greg was informed after Sam (I'm assuming the various bits being flung about by Swisher are true; she gets a free pass on things like this), so I think the sequence was: a subset of the board meets, forms quorum, votes to terminate Sam and remove Greg as chair (without telling him). Then they write the PR, and around the same time, let Sam and then Greg know. If OpenAI were a government, this would be called a coup.
>>brohee+pg
Rushing out a press release with vague accusations and without consulting the relevant parties certainly feels more like a coup than a traditional vote of no confidence.