I disagree, this is pretty standard practice in civil and criminal cases. In the event that both sides undergo discovery, if settlement is reached, it’s going to be on the eve of trial/arbitration. It’s a way for both sides to get what they want. The state gets to say, “we got them to admit it!” The defendants will get to say (despite the Judge’s assertions that the agreement is open ended for punishment, I expect neither will see jail time), “we avoided jail time!”
It wouldn’t surprise me if Spanier pleads guilty to lesser charges this week too. It’s just the nature of the criminal field, especially when significant jail time is being faced.