Devil's Play... But How?

I am slowly winding down to finishing my first playthrough of WotR, and I came across something that I am not sure if it is a glitch or some weird element of the game that I'm not immediately familiar with.

After leaving Iz, with Queen Galfrey having kicked the bucket, I began sweeping up some side quests/locations I haven't done yet. Whether or not it appeared before or after completing Iz, I'm not sure; but an area popped up labeled "A Trap for a Queen."

I was confused but entered anyway, buffing up all of my party prepared for some sort of fight. I figured maybe it was a trap for the queen in the event she had left alive?

But no. She is totally alive and talking to me. There's some demon guy I swear I've never ran into but I'm not certain across this long campaign, and it is totally a setup from my character somehow.

I ended up reloading and all of my efforts googling to figure out what happened hasn't found me any luck. I'm still trying to dodge some spoilers myself; like I said, this is my first blind playthrough. A new quest popped up and everything titled "Devil's Play" but that brought back no results at all.

I've gotten some information about other mythic paths but mostly the confusing part is when did I accidentally set up a betrayal? Don't get me wrong, I'm an Angel who has no love lost for Galfrey, but I don't think at any point I actively picked this route. It's hard to know which locations are worth going when half of them give me puzzle pieces as a reward, but this seems off. Any answers would be great.