My theory is that a wealthy crime family moved in to the house in 1974, did it up very high spec for that era,, had a few happy years there, but had to flee the country when a dodgy deal went wrong circa 1982 (roughly around the time people stopped buying the Encyclopaedia Britannica in instalments, which I notice takes pride of place on the bookshelves, and started buying black leather sofas).
The family photo of the garden looks a bit grainy, too. I believe it was taken in a time before digital cameras 
. A time when rich people had landline phones by their bedside and those massive TVs they wheeled out at school were really cool (having one in your bedroom would certainly have been an unheard of luxury).
They have only just been able to come out of hiding and sort out their affairs, so the house has been perfectly preserved in a land that time forgot.
I bet there is money hidden underneath the floorboards