I got a response from a playtester:
"I believe you ruled correctly Sergio. An effect that's cancelled is still considered to be resolved (ie that's how it was resolved, by nothing happening) and the card is considered played even if the effect is cancelled. Many a discussion was had along those lines."
So, some things to glean from the discussion:
1) Yes, in order for a card to be considered played, it must specifically meet all of the 3 criteria set forth -
a) the resource cost must be paid (and additional costs such as discarding if necessitated by the card).
b) it must be transfered into play OR it's EFFECT MUST RESOLVE
c) it must be discarded if it is an event card
ALL of these criteria must be met for the card to have been considered played. I only emphasize that so much because that definition of played is remarkably different from any other CCGs/TCGs I've played.
2) An effect that is cancelled still resolves. You resolve the effect by doing nothing; it has no result. Therefore, an event card whose effect has been cancelled does meet all three criteria of having been played.
So, I owe a bit of an apology to whomever wrote the rules. There is no "unfortunate wording" of the criteria set forth for what qualifies as played. Rather, the most intricately crafted mechanic and set of terms I have ever encountered in any game of this sort when dealing with the concept of playing and "countering" cards/effects has been written.
I mean, consider how it actually works:
A player initiates the sequence of playing an event (that's how you have to phrase it, because technically it's not played until its effect resolves).
The opponent initiates the sequece of playing another card that is an interrupt.
The interrupt resolves first, cancelling an effect…of a card that technically has not even been played yet.
The interrupt is then considered to have been played.
The initial event resolves. It's effect is nothing.
The initial event is then considered to have been played.
I've really never seen any timing or definitions of those aspects of the game like that.