Why is Jabalia called 'Gaza's biggest refugee camp'? Isn't Gaza one big, singular refugee camp?

Jabalia was leveled by the IDF in the past day. The media is reporting that this was an attack on 'Gaza's largest refugee camp'. Most of Gaza's population have been classified by UNRWA as refugees for decades, if not because of the 1948 war, then because of the 1967 war. The population has been internally displaced by continued wars since then, so the few Gazans that lived there before 1948 are almost certainly refugees now.