A note in the attic reveals that the Shadow Puzzles were installed by Trevor and Chamberlain Construction, a nod to the architect of the mansions in previous Resident Evil games, George Trevor.
There is a newspaper article in the Main Hall written by Alyssa Ashcroft, a character from Resident Evil Outbreak.
You can find a book called The Unveiled Abyss written by Clive R. O’Brien, a character from Resident Evil: Revelations.
The ghosts in the demo are a nod to Sweet Home, the game that the original Resident Evil started off as a remake of before becoming a new IP.
There is a picture in the Main Hall of the Arklay Mountains, the location of the mansion from the first Resident Evil game.