http://wccftech.com/fortnite-ps4xo-crossplay-mistake-spencer/

Crossplay between PS4 and Xbox One players was briefly available in Epic Games’ Fornite, but the publisher states that this was a mistake.

Reports about Fortnite PS4 players playing against Xbox One players surfaced this weekend. At first it seemed that it was merely a case of PC players battling PS4 players, but this was soon corrected as proof of PS4/Xbox One crossplay was posted on Reddit.