That is because in 1943 Josiah Samuels wrote an influential book called, "Into the Fortnite" that depicted characters who were involved in a long, protracted battle. Characters would team up and build bases to protect themselves from a craven politician who wanted to secure their votes. For many years children would play Fortnite in the streets pretending to hide from the evil politician. Eventually, this game became quite popular to the point of achieving household ubiquity. A lot of older folks get confused and think this game was a video game!