Every DLC character thus far has been in the game's coding prior to the release of the DLC and due to this, the characters were known long before the release of the DLC. What you download is really just unlocking the characters and weapons. I actually knew of every DLC character, weapon, and pet months prior to their release due to leaks related to this. This is also why people believe that there will be no more new DLC, every character from the game's coding is now available. Every character currently available has been in the game's coding since launch, if there were to be any more (i.e. the pink knight), they would have to add to the game's coding, a full-fledged DLC, not just an unlock. The fact that every character is in the coding however, is also why people who have the DLC can play with people who do not. This is also why the DLC downloads are so small, it isn't adding anything, just unlocking it.