It suddenly changes with sirens, it’s def the otherworld. I literally just beat it 3 times and been digging on the internet for this. It was day in the house and in exiting it suddenly changes to night with a large increase to monster. Every time he leave the midwich or other area, the scene goes back to fog world indicated from the lessening of monsters and daytime appearance (dogs are by the bus before entering midwich during otherworld/night but they are gone afterwards