One of the ghosts in this haunted building must have been a gamer, because the mysterious message on the chalkboard at 2:36 is an obvious reference to the video game "Portal".
In the game, you assume the role of a test subject who must solve a Kafkaesque series of physical puzzles in order to escape from a sinister science lab. The artificial intelligence who controls the lab promises that "there will be cake" when you have completed all of the tests. As you progress through the game, you find messages that previous test subjects have scrawled upon the walls, one of which says "the cake is a lie".
Although this expression may have an alternate historical context, I'm pretty sure that these clueless ghost hunters were duped by a mischievous Portal player.
See them make fools of themselves in this news story from KJRH in Tulsa, Oklahoma:http://youtu.be/dXVNvfPetxU