Hi, I think I discovered something. (not game changing but hey, it's still something)
I don't really know what triggers it, but here are the steps I followed :
Take the stair of the saloon (take the left stair)
Go all the way of the top until you're next to the right stair, at the top.
Then, try doing stupid things, because idk what triggers it really.
Though it is really simple to trigger whatever the ♥♥♥♥ you trigger.
I made a little video for you because I'm explaining it very bad (i pause it before the ""jumpscare"") : https://www.youtube.com/watch?v=OGjU9eiTARM