If I had a Kurgadon and a Didgeridoo, hacked to say "beast" instead of "minotaur" with Artificial Evolution, in play, and I used Didgeridoo to put Symbiotic Beast into play, would Kurgadon's ability trigger?
I am thinking no, since I am not casting the Symbiotic Beast, just putting it into play.
Reading the gatherer wording for older cards can make the analysis easier.
{3}: You may put a Minotaur permanent card from your hand onto the battlefield.
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.
Casting refers only to putting spells on the stack, not moving cards from one zone to another by other means.
601.2. To cast a spell is to take it from where it is (usually the hand), put it on the stack, and pays its costs, so that it will eventually resolve and have its effect.
In this case, you're putting an ability activation on the stack, but the card in question goes directly from your hand to the battlefield, so nothing is cast.
(Note also that casting refers to moving the object onto the stack — objects created on the stack, like storm copies, also aren't "cast".)
