Some things I noticed about the River King's tale

So we've all seen the video by now and we're all drawing hypothesis, but I couldn't help but be drawn to a few things in particular. A few lines that just really stuck out to me.

The first was "And thus she failed to recognize when that demon's jaw unhinged". Someone clarify for me here, but has the word demon ever appeared in the lore? I feel like this is the first time. I feel like that's important, not necessarily to the River King, but to the world as a whole. Who in Runeterra believes in demons? More to the point does Runeterra actually have demons? Aatrox looks like one to us but he's a Darkin and has never been described as demonic in any way, no one has-no wait I remember Shaco. He's referred to as the Demon Jester, but aside from his title I've never seen the word used, and I feel that has greater implications. Might be me grasping at straws but who knows?

On to things relating more to the River King himself, I wanna draw to the actual interactions he had with the two people in the story; the gambler and the bride. The Bride says "Not now, not this time!" implying this isn't the first time his majesty has ruined the party or deposed of a suitor of hers. He supports this by saying "but it's the last time I swear, so please forgive." So he had dealings with her before, for sure, implying that she made a bargain with him like the gambler, what was that deal I wonder, and more, to the point could this mean this woman had people constantly introduced in to her life and then ripped away from her by his royal highness of the rivers?

On to the Gambler; twice the King talks about being "Let in", implying something was keeping him out. Going back to the notion that the woman had dealings with the River King in the past, this could imply that the whole deal with the Gambler wasn't just to ruin the Gambler's life but to get at someone he'd also made a bargain with; the bride. He ruins two lives at once, all for personal satisfaction.

Some thoughts and musings on my part, but what do you guys recon?

Also I'm gonna call it now: The gambler ain't TF, the bride ain't Eve. Calling it. We've been through this before with the thug from Ekko: Seconds being Urgot/Singed or otherwise and he wasn't.