I'll say what I said in the main comment section, this seems like a distinction without a real difference, right after it says he paid 5.2 million, it says "virtually all liability was washed away when he filed". That seems to indicate he got his taxes down to $750, and instead of a refund, just had the money he paid put to cover future taxes, which might also get reduced for refunded at a later date. He still paid $750 for 2016 and 2017, he just also added a down payment for future taxes, which he might get refunded if he continues to only pay $750 each year.

There are only two ways to frame this. That he paid 5.2 million in taxes 2016 and 2017 and that now allows him to not pay taxes at all for the next unforeseen few years, or that he paid $750 both years and put a down payment for any future taxes he might get back, neither of which is good.

He doesn't have to, but for all we know he may overpay again. He overpaid two years in a row according to this article. We can't fault him on something he has or hasn't done yet.