If I were to "cheat" a card into play, would Kurgadon activate?
Reading the gatherer wording for older cards can make the analysis easier.

Didgeridoo:


  {3}: You may put a Minotaur permanent card from your hand onto the battlefield.


Kurgadon


  Whenever you cast a creature spell with converted mana cost 6 or greater, put three +1/+1 counters on Kurgadon.


So you are correct, clearly the Didgeridoo does not cast a creature spell, so the Kurgadon's ability will not trigger.