Apparently, it appears that Prime Minister Tsipiras' impulsive move to evade leadership responsibilities pulled the rug out from his negotiators who were still talking when he made his move. From Bloomberg.com:
Shortly before midnight on Friday in the Belgian capital, the Greeks and representatives of the European Union and International Monetary Fund, tucked away in the EU Commission’s Charlemagne building, learned via Twitter that their efforts were in vain, according to an EU official.
It was the first time Prime Minister Alexis Tsipras’s Brussels negotiators had heard about it. They soon left the room, their attempts to thrash out a compromise in tatters.
Greeks Working on Deal Blindsided by Twitter Post on Referendum - Bloomberg Business