Listened to the episode again. Tim mentioned the grandmother's belongings were in the house, so perhaps Jay's grandmother may have died or perhaps be in care, hence the state of the property. It may be that Jays family no longer owned the property in 1992 and they rented off the new owner, hence Jay being unfamiliar with the Uncle Jack story.
One thought: If Jack was getting out the window because the door was locked, how once the window was nailed shut did he get out onto the landing...?
At present I feel there was poltergeist activity but they may have played on this to provide an excuse to end the cheap rent + renovations agreement and move out