Yes you are missing a little detail. He is paying tax on exercising options which he was awarded as part of his salary. He does not owe the money because the co

Yes you are missing a little detail. He is paying tax on exercising options which he was awarded as part of his salary. He does not owe the money because the company went public but because he chose to exercise the options. He could exercise less options and pay less taxes. And the fact that he can exercise the options usually means that he can sell the resulting shares.