That's common practice.
It's also common to work out the string and take the equivalent of the banked vacation days as a cash going-away present. Most private companies limit the number of vacation days you can carry forward; AFAIK many government agencies don't.
I'm not surprised though, that he was allowed to use the stored vacation cushion to bridge the gap between today's resignation/firing and his retirement date.
There ought to be a clawback provision if he's found to have been as naughty as we think he was.
Lol, really? Why would he do that when he could simply show up to work each day for another month or so and get paid, and when he retires SELL his unused leave time back to the gov, and get paid for I as well?
Besides he had already said earlier he was staying on until March.