Factual error: The moving truck that transports the Perron family's belongings didn't exist in 1971. It is a 1973 model or newer.
Factual error: The morning after the exorcism, the headlights on all the cars outside of the house are still on. There is no way car batteries from the 1970s would have lasted all night.
Answer: The demon takes control of the witch. The witch likely opened a portal for the demon who attached to the witch. As such, the demon still hasn't walked the earth itself.
Ssiscool ★