[2020] Interaction with Enemy of Enlightenment?

So, in a draft I was facing an [[Enemy of Enlightenment]], had 2 cards in hand making him a 3/3, and one of those cards was [[Triumphant Surge]] that kills creatures with power 4 or greater. I decided to try it, and the moment I clicked to cast the card, the creature became a 4/4 and I was able to kill it.

Is this how it´s suppose to work? The card leaves your hand before you choose valid targets? I don´t recall, but I believe there were another valid targets on the board. Would it even be possible to try to cast it if that 3/3 creature was the only thing on board?

btw sorry for creating a post, couldn´t find the weekly FAQ thread