Getting the very serious offer from Twitter was the best thing to happen to Neal.
I can only imagine the negotiation with Google that he must of had. It probably went on the lines of something like this -
"Hey, I really love it here at Google. I am really excited with what we are working on and want to deliver it but this Twitter offer is just something that I can't ignore. I am looking at the financial future of my family and I would be doing them a disservice if I don't consider this offer seriously. Is there anything we can do to just make this offer go away."
Neal had the upper hand. Worst-case scenario for him would be that there would be no change. He would continue to work at Google. Next best case scenario would be that he would be working at another mega-tech company, and getting better compensated with potentially even greater upside.
Google was in a position of weakness in either case. If they did nothing and he left, it would amount to even more collateral damage as others would get the message that Google can't compete and Twitter would make even more offers to others.
By paying him out, they basically paid him the opportunity cost in real dollars that he may have had if he moved to Twitter.
In all of this, Neal's professionalism would have tipped the favor on his side.