The OP could be mistaken about the cat that she sees sitting in the window. It could be like our cat - a house cat by day (her choice - she has a cat flap!) but she will go out all night when she wants to. especially in the Summer.
My daughter has 2 cats - brothers - one goes out a lot, the other only goes out when he has to - again, their choice as they have a cat flap. I'll swear the one that stays in thinks he's human - he watched over the children as they slept in their cribs as babies and is a really loving, soppy cat.
Frank Field, Labour Peer has died, aged 81y.