Classic power play and shrewd negotiation tactic. They probably felt all the hours talking over 3 days, the time crunch, the continued loss of money, and most significantly the owners' willingness to sacrifice the season had led to the obvious conclusion the players' 53 line in the sand was a pie in the sky. My guess is the owners said 50/50 with the belief the players, finally accepting defeat, would come back at 51 so an actual deal could be made.
The problem in this scenario is the players have very bad leadership. The owners are putting it out there that they'll deal at 51, they have the winning hand, and the players need to get what they can. But the players (read: Hunter) won't accept that which is why this is still unresolved. It sucks to lose in life, but you have to understand when failure is inevitable, and then make the most of that.
From the Press Conference on NBATV Billy Hunter made it sound like it was agree to 50/50 or else. He even said that later the owners refuted actually saying that, but even the mediator had written it down in his chat notebook.