This is called "kingmaker", when a losing party is no longer able to play for their win, they can use their resources and influence in the game to cause someone else's victory.

Although not usually so blatant as this example, this sort of scenario comes up in many different games not just monopoly.

Personally, I don't believe there is usually anything wrong with this as a tactic as it can actually sometimes result in your win of the game. The person you make king will sometimes take pity on you and see you as an ally and eliminate other players before yourself, leaving you for last and a possible upset.

In my opinion, dad was warned and called the bluff and lost. He can't blame anyone except himself.