[They overbooked the flight]
It is mentioned above that United did not overbook the flight, though I expect any overbooking was taken care of before boarding like usual so I don't think overbooking was a factor in this instance yet some people still want to hold United accountable for overbooking.
[did not manage the logistics of staff needed and how to transport them.]
Isn't that exactly what they did by deadheading four crew at the last minute?  Are you holding them to some unrealistic expectation to have reserve staff at every airport United lands planes all over the world?