From the SEC filing linked below, this compensation was primarily because Yahoo gave him a large number of RSUs upon joining to make up for compensation he was

From the SEC filing linked below, this compensation was primarily because Yahoo gave him a large number of RSUs upon joining to make up for compensation he was giving up by leaving Google. Otherwise he would have lost money by taking the new job. Those "make-whole" RSUs then vested early upon termination, which is good negotiating, but not surprising. He also got performance options, which were granted upon termination because he met the performance goals of the stock price.