It's an aggregation of previous leaks. Malicious actors having all that information together is a big deal in and of itself, but it's not the"mother of all breaches" some publications are trying to make it be.
This, i keep telling people this is just a very sensationalized headline. Some of the companies listed here are definitely from breaches that happened over 5 years ago (ex: myfitnesspal)
The Naz.API leak that was given to Troy Hunt is different from this leak. That's also an aggregation, but smaller in size. What Troy has is probably more significant since about 1/3 of that is newly discovered. Right now, no one has published an analysis of the unique accounts in this larger aggregation.