No, the Yeti raid in Chyllfroest is unrelated to the Yeti raid in Folda, they have separate time windows which don't interfere with each other, as shown in data of Yetis killed 2 days in a row.
Yes, you should treat them as two separate spawns and, if you're trying to find a Yeti you should keep looking on both spawns.
It's difficult to ascertain the exact window on the Chyllfroest spawn, since you have no way of knowing in which spawn a Yeti died last unless you have killed him yourself or know who did, kind of like it happens with Crustacea Gigantica, Albino Dragon, Rotworm Queen, among others.. My advice is to keep checking on both spawns until event is over.
Good luck and happy hunting!